Here it is (anonymized). I can privately provide the domain if there is a way to do so.
2017-06-20 21:37:55 0 [cert4android.CustomCertManager$1] Connected to service
2017-06-20 21:37:55 1 [syncadapter.SyncAdapterService$SyncAdapter] at.bitfire.davdroid.addressbooks sync of Account {name=dummy@email.com, type=bitfire.at.davdroid} has been initiated.
PARAMETER #1 = ignore_settings
PARAMETER #2 = force
PARAMETER #3 = expedited
PARAMETER #4 = ignore_backoff
2017-06-20 21:37:55 1 [AccountSettings] Account dummy@email.com has version 6, current version: 6
2017-06-20 21:37:55 1 [syncadapter.AddressBooksSyncAdapterService$AddressBooksSyncAdapter] Running sync for address book
PARAMETER #1 = Account {name=Contacts (dummy@email.com kQ), type=at.bitfire.davdroid.address_book}
2017-06-20 21:37:55 1 [syncadapter.AddressBooksSyncAdapterService$AddressBooksSyncAdapter] Address book sync complete
2017-06-20 21:37:55 1 [syncadapter.SyncAdapterService$SyncAdapter] Sync for at.bitfire.davdroid.addressbooks complete
2017-06-20 21:37:55 2 [syncadapter.SyncAdapterService$SyncAdapter] com.android.contacts sync of Account {name=Contacts (dummy@email.com kQ), type=at.bitfire.davdroid.address_book} has been initiated.
PARAMETER #1 = ignore_settings
PARAMETER #2 = force
PARAMETER #3 = expedited
PARAMETER #4 = ignore_backoff
2017-06-20 21:37:55 2 [AccountSettings] Account dummy@email.com has version 6, current version: 6
2017-06-20 21:37:55 2 [syncadapter.ContactsSyncAdapterService$ContactsSyncAdapter] Synchronizing address book: https://nextcloud10.mydomain.com/remote.php/dav/addressbooks/users/dummy.user/contacts/
2017-06-20 21:37:55 2 [syncadapter.ContactsSyncAdapterService$ContactsSyncAdapter] Taking settings from: Account {name=dummy@email.com, type=bitfire.at.davdroid}
2017-06-20 21:37:55 2 [syncadapter.SyncManager] Preparing synchronization
2017-06-20 21:37:56 2 [syncadapter.SyncManager] Querying capabilities
2017-06-20 21:37:56 2 [HttpClient$1] --> PROPFIND https://nextcloud10.mydomain.com/remote.php/dav/addressbooks/users/dummy.user/contacts/ http/1.1
2017-06-20 21:37:56 2 [HttpClient$1] Content-Type: application/xml; charset=utf-8
2017-06-20 21:37:56 2 [HttpClient$1] Content-Length: 258
2017-06-20 21:37:56 2 [HttpClient$1] Depth: 0
2017-06-20 21:37:56 2 [HttpClient$1]
2017-06-20 21:37:56 2 [HttpClient$1] <?xml version=‘1.0’ encoding=‘UTF-8’ ?><propfind xmlns=“DAV:” xmlns:CAL=“urn:ietf:params:xml:ns:caldav” xmlns:CARD=“urn:ietf:params:xml:ns:carddav”><prop><CARD:supported-address-data /><n0:getctag xmlns:n0=“http://calendarserver.org/ns/” /></prop></propfind>
2017-06-20 21:37:56 2 [HttpClient$1] --> END PROPFIND (258-byte body)
2017-06-20 21:37:56 3 [syncadapter.SyncAdapterService$SyncAdapter] com.android.calendar sync of Account {name=dummy@email.com, type=bitfire.at.davdroid} has been initiated.
PARAMETER #1 = ignore_settings
PARAMETER #2 = force
PARAMETER #3 = expedited
PARAMETER #4 = ignore_backoff
2017-06-20 21:37:56 3 [AccountSettings] Account dummy@email.com has version 6, current version: 6
2017-06-20 21:37:56 3 [syncadapter.CalendarsSyncAdapterService$SyncAdapter] Updating local calendar https://nextcloud10.mydomain.com/remote.php/dav/calendars/dummy.user/defaultcalendar_shared_by_another.user/ with CollectionInfo(id=22, serviceID=6, type=null, url=https://nextcloud10.mydomain.com/remote.php/dav/calendars/dummy.user/defaultcalendar_shared_by_another.user/, readOnly=false, displayName=AnotherUser(another.user), description=AnotherUser, color=-1146130, timeZone=null, supportsVEVENT=true, supportsVTODO=true, selected=true, confirmed=false)
2017-06-20 21:37:56 2 [cert4android.CustomCertManager] Certificate not trusted by system
2017-06-20 21:37:56 2 [cert4android.CustomCertManager] Querying custom certificate trustworthiness
2017-06-20 21:37:56 3 [syncadapter.CalendarsSyncAdapterService$SyncAdapter] Updating local calendar https://nextcloud10.mydomain.com/remote.php/dav/calendars/dummy.user/privat/ with CollectionInfo(id=24, serviceID=6, type=null, url=https://nextcloud10.mydomain.com/remote.php/dav/calendars/dummy.user/privat/, readOnly=false, displayName=MyUserName, description=MyUserName, color=-6306073, timeZone=null, supportsVEVENT=true, supportsVTODO=true, selected=true, confirmed=false)
2017-06-20 21:37:56 3 [syncadapter.CalendarsSyncAdapterService$SyncAdapter] Synchronizing calendar #4, URL: https://nextcloud10.mydomain.com/remote.php/dav/calendars/dummy.user/defaultcalendar_shared_by_another.user/
2017-06-20 21:37:56 3 [syncadapter.SyncManager] Preparing synchronization
2017-06-20 21:37:56 3 [syncadapter.SyncManager] Querying capabilities
2017-06-20 21:37:56 3 [HttpClient$1] --> PROPFIND https://nextcloud10.mydomain.com/remote.php/dav/calendars/dummy.user/defaultcalendar_shared_by_another.user/ http/1.1
2017-06-20 21:37:56 3 [HttpClient$1] Content-Type: application/xml; charset=utf-8
2017-06-20 21:37:56 3 [HttpClient$1] Content-Length: 227
2017-06-20 21:37:56 3 [HttpClient$1] Depth: 0
2017-06-20 21:37:56 3 [HttpClient$1]
2017-06-20 21:37:56 3 [HttpClient$1] <?xml version=‘1.0’ encoding=‘UTF-8’ ?><propfind xmlns=“DAV:” xmlns:CAL=“urn:ietf:params:xml:ns:caldav” xmlns:CARD=“urn:ietf:params:xml:ns:carddav”><prop><n0:getctag xmlns:n0=“http://calendarserver.org/ns/” /></prop></propfind>
2017-06-20 21:37:56 3 [HttpClient$1] --> END PROPFIND (227-byte body)
2017-06-20 21:37:56 3 [cert4android.CustomCertManager] Certificate not trusted by system
2017-06-20 21:37:56 3 [cert4android.CustomCertManager] Querying custom certificate trustworthiness
2017-06-20 21:44:55 3 [HttpClient$1] <-- HTTP FAILED: javax.net.ssl.SSLHandshakeException: Timeout when waiting for certificate trustworthiness decision
2017-06-20 21:44:55 3 [syncadapter.SyncManager] I/O exception during sync, trying again later
EXCEPTION javax.net.ssl.SSLHandshakeException: Timeout when waiting for certificate trustworthiness decision
at com.android.org.conscrypt.OpenSSLSocketImpl.startHandshake(OpenSSLSocketImpl.java:357)
at okhttp3.internal.connection.RealConnection.connectTls(RealConnection.java:281)
at okhttp3.internal.connection.RealConnection.establishProtocol(RealConnection.java:251)
at okhttp3.internal.connection.RealConnection.connect(RealConnection.java:151)
at okhttp3.internal.connection.StreamAllocation.findConnection(StreamAllocation.java:192)
at okhttp3.internal.connection.StreamAllocation.findHealthyConnection(StreamAllocation.java:121)
at okhttp3.internal.connection.StreamAllocation.newStream(StreamAllocation.java:100)
at okhttp3.internal.connection.ConnectInterceptor.intercept(ConnectInterceptor.java:42)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:92)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:67)
at okhttp3.internal.cache.CacheInterceptor.intercept(CacheInterceptor.java:93)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:92)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:67)
at okhttp3.internal.http.BridgeInterceptor.intercept(BridgeInterceptor.java:93)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:92)
at okhttp3.internal.http.RetryAndFollowUpInterceptor.intercept(RetryAndFollowUpInterceptor.java:120)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:92)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:67)
at okhttp3.logging.HttpLoggingInterceptor.intercept(HttpLoggingInterceptor.java:211)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:92)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:67)
at okhttp3.RealCall.getResponseWithInterceptorChain(RealCall.java:185)
at okhttp3.RealCall.execute(RealCall.java:69)
at at.bitfire.dav4android.DavResource.propfind(DavResource.kt:264)
at at.bitfire.davdroid.syncadapter.CalendarSyncManager.queryCapabilities(CalendarSyncManager.java:90)
at at.bitfire.davdroid.syncadapter.SyncManager.performSync(SyncManager.java:141)
at at.bitfire.davdroid.syncadapter.CalendarsSyncAdapterService$SyncAdapter.sync(CalendarsSyncAdapterService.java:68)
at at.bitfire.davdroid.syncadapter.SyncAdapterService$SyncAdapter.onPerformSync(SyncAdapterService.java:85)
at android.content.AbstractThreadedSyncAdapter$SyncThread.run(AbstractThreadedSyncAdapter.java:272)
Caused by: java.security.cert.CertificateException: Timeout when waiting for certificate trustworthiness decision
at at.bitfire.cert4android.CustomCertManager.checkCustomTrusted$cert4android_release(CustomCertManager.kt:222)
at at.bitfire.cert4android.CustomCertManager.checkServerTrusted(CustomCertManager.kt:163)
at com.android.org.conscrypt.Platform.checkServerTrusted(Platform.java:117)
at com.android.org.conscrypt.OpenSSLSocketImpl.verifyCertificateChain(OpenSSLSocketImpl.java:643)
at com.android.org.conscrypt.NativeCrypto.SSL_do_handshake(Native Method)
at com.android.org.conscrypt.OpenSSLSocketImpl.startHandshake(OpenSSLSocketImpl.java:353)
… 28 more
2017-06-20 21:44:55 3 [syncadapter.CalendarsSyncAdapterService$SyncAdapter] Synchronizing calendar #5, URL: https://nextcloud10.mydomain.com/remote.php/dav/calendars/dummy.user/privat/
2017-06-20 21:44:55 3 [syncadapter.SyncManager] Preparing synchronization
2017-06-20 21:44:55 3 [syncadapter.SyncManager] Querying capabilities
2017-06-20 21:44:55 3 [HttpClient$1] --> PROPFIND https://nextcloud10.mydomain.com/remote.php/dav/calendars/dummy.user/privat/ http/1.1
2017-06-20 21:44:55 3 [HttpClient$1] Content-Type: application/xml; charset=utf-8
2017-06-20 21:44:55 3 [HttpClient$1] Content-Length: 227
2017-06-20 21:44:55 3 [HttpClient$1] Depth: 0
2017-06-20 21:44:55 3 [HttpClient$1]
2017-06-20 21:44:55 3 [HttpClient$1] <?xml version=‘1.0’ encoding=‘UTF-8’ ?><propfind xmlns=“DAV:” xmlns:CAL=“urn:ietf:params:xml:ns:caldav” xmlns:CARD=“urn:ietf:params:xml:ns:carddav”><prop><n0:getctag xmlns:n0=“http://calendarserver.org/ns/” /></prop></propfind>
2017-06-20 21:44:55 3 [HttpClient$1] --> END PROPFIND (227-byte body)
2017-06-20 21:44:55 3 [cert4android.CustomCertManager] Certificate not trusted by system
2017-06-20 21:44:55 3 [cert4android.CustomCertManager] Querying custom certificate trustworthiness
2017-06-20 21:44:56 2 [HttpClient$1] <-- HTTP FAILED: javax.net.ssl.SSLHandshakeException: Timeout when waiting for certificate trustworthiness decision
2017-06-20 21:44:56 2 [syncadapter.SyncManager] I/O exception during sync, trying again later
EXCEPTION javax.net.ssl.SSLHandshakeException: Timeout when waiting for certificate trustworthiness decision
at com.android.org.conscrypt.OpenSSLSocketImpl.startHandshake(OpenSSLSocketImpl.java:357)
at okhttp3.internal.connection.RealConnection.connectTls(RealConnection.java:281)
at okhttp3.internal.connection.RealConnection.establishProtocol(RealConnection.java:251)
at okhttp3.internal.connection.RealConnection.connect(RealConnection.java:151)
at okhttp3.internal.connection.StreamAllocation.findConnection(StreamAllocation.java:192)
at okhttp3.internal.connection.StreamAllocation.findHealthyConnection(StreamAllocation.java:121)
at okhttp3.internal.connection.StreamAllocation.newStream(StreamAllocation.java:100)
at okhttp3.internal.connection.ConnectInterceptor.intercept(ConnectInterceptor.java:42)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:92)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:67)
at okhttp3.internal.cache.CacheInterceptor.intercept(CacheInterceptor.java:93)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:92)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:67)
at okhttp3.internal.http.BridgeInterceptor.intercept(BridgeInterceptor.java:93)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:92)
at okhttp3.internal.http.RetryAndFollowUpInterceptor.intercept(RetryAndFollowUpInterceptor.java:120)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:92)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:67)
at okhttp3.logging.HttpLoggingInterceptor.intercept(HttpLoggingInterceptor.java:211)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:92)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:67)
at okhttp3.RealCall.getResponseWithInterceptorChain(RealCall.java:185)
at okhttp3.RealCall.execute(RealCall.java:69)
at at.bitfire.dav4android.DavResource.propfind(DavResource.kt:264)
at at.bitfire.davdroid.syncadapter.ContactsSyncManager.queryCapabilities(ContactsSyncManager.java:172)
at at.bitfire.davdroid.syncadapter.SyncManager.performSync(SyncManager.java:141)
at at.bitfire.davdroid.syncadapter.ContactsSyncAdapterService$ContactsSyncAdapter.sync(ContactsSyncAdapterService.java:68)
at at.bitfire.davdroid.syncadapter.SyncAdapterService$SyncAdapter.onPerformSync(SyncAdapterService.java:85)
at android.content.AbstractThreadedSyncAdapter$SyncThread.run(AbstractThreadedSyncAdapter.java:272)
Caused by: java.security.cert.CertificateException: Timeout when waiting for certificate trustworthiness decision
at at.bitfire.cert4android.CustomCertManager.checkCustomTrusted$cert4android_release(CustomCertManager.kt:222)
at at.bitfire.cert4android.CustomCertManager.checkServerTrusted(CustomCertManager.kt:163)
at com.android.org.conscrypt.Platform.checkServerTrusted(Platform.java:117)
at com.android.org.conscrypt.OpenSSLSocketImpl.verifyCertificateChain(OpenSSLSocketImpl.java:643)
at com.android.org.conscrypt.NativeCrypto.SSL_do_handshake(Native Method)
at com.android.org.conscrypt.OpenSSLSocketImpl.startHandshake(OpenSSLSocketImpl.java:353)
… 28 more
2017-06-20 21:44:56 2 [syncadapter.ContactsSyncAdapterService$ContactsSyncAdapter] Contacts sync complete
2017-06-20 21:44:56 2 [syncadapter.SyncAdapterService$SyncAdapter] Sync for com.android.contacts complete
2017-06-20 21:46:30 4 [syncadapter.SyncAdapterService$SyncAdapter] com.android.contacts sync of Account {name=Contacts (dummy@email.com kQ), type=at.bitfire.davdroid.address_book} has been initiated.
2017-06-20 21:46:30 4 [AccountSettings] Account dummy@email.com has version 6, current version: 6
2017-06-20 21:46:30 4 [syncadapter.ContactsSyncAdapterService$ContactsSyncAdapter] Synchronizing address book: https://nextcloud10.mydomain.com/remote.php/dav/addressbooks/users/dummy.user/contacts/
2017-06-20 21:46:30 4 [syncadapter.ContactsSyncAdapterService$ContactsSyncAdapter] Taking settings from: Account {name=dummy@email.com, type=bitfire.at.davdroid}
2017-06-20 21:46:30 4 [syncadapter.SyncManager] Preparing synchronization
2017-06-20 21:46:30 4 [syncadapter.SyncManager] Querying capabilities
2017-06-20 21:46:30 4 [HttpClient$1] --> PROPFIND https://nextcloud10.mydomain.com/remote.php/dav/addressbooks/users/dummy.user/contacts/ http/1.1
2017-06-20 21:46:30 4 [HttpClient$1] Content-Type: application/xml; charset=utf-8
2017-06-20 21:46:30 4 [HttpClient$1] Content-Length: 258
2017-06-20 21:46:30 4 [HttpClient$1] Depth: 0
2017-06-20 21:46:30 4 [HttpClient$1]
2017-06-20 21:46:30 4 [HttpClient$1] <?xml version=‘1.0’ encoding=‘UTF-8’ ?><propfind xmlns=“DAV:” xmlns:CAL=“urn:ietf:params:xml:ns:caldav” xmlns:CARD=“urn:ietf:params:xml:ns:carddav”><prop><CARD:supported-address-data /><n0:getctag xmlns:n0=“http://calendarserver.org/ns/” /></prop></propfind>
2017-06-20 21:46:30 4 [HttpClient$1] --> END PROPFIND (258-byte body)
2017-06-20 21:46:30 4 [cert4android.CustomCertManager] Certificate not trusted by system
2017-06-20 21:46:30 4 [cert4android.CustomCertManager] Querying custom certificate trustworthiness