Verified both with Kolab Now, as well as our corporate Kolab Server:

Issue occurs for calendars only, tasks seem to sync fine.
Debug log:
I/davdroid.SyncManager( 7664): Uploading 0 modified resource(s) (if not changed)
I/davdroid.SyncManager( 7664): Synchronization forced
I/davdroid.SyncManager( 7664): Fetching remote resource list
D/HttpClient( 7664): Re-using cached 'basic' auth scheme for https://apps.kolabnow.com:443
D/HttpClient( 7664): Connection request: [route: HttpRoute[{s}->https://apps.kolabnow.com:443]][total kept alive: 1; route allocated: 1 of 2; total allocated: 1 of 3]
D/HttpClient( 7664): Connection leased: [id: 5][route: HttpRoute[{s}->https://apps.kolabnow.com:443]][total kept alive: 0; route allocated: 1 of 2; total allocated: 1 of 3]
D/HttpClient( 7664): Executing request REPORT /calendars/greve@georggreve.net/c81425b202e6-3182008d3351-2712f63c/ HTTP/1.1
D/HttpClient( 7664): Target auth state: CHALLENGED
D/HttpClient( 7664): Proxy auth state: UNCHALLENGED
D/Wire ( 7664): http-outgoing-5 >> "REPORT /calendars/greve@georggreve.net/c81425b202e6-3182008d3351-2712f63c/ HTTP/1.1[\r][\n]"
D/Wire ( 7664): http-outgoing-5 >> "Content-Type: text/xml; charset=UTF-8[\r][\n]"
D/Wire ( 7664): http-outgoing-5 >> "Accept: text/xml[\r][\n]"
D/Wire ( 7664): http-outgoing-5 >> "Depth: 1[\r][\n]"
D/Wire ( 7664): http-outgoing-5 >> "Content-Length: 260[\r][\n]"
D/Wire ( 7664): http-outgoing-5 >> "Host: apps.kolabnow.com[\r][\n]"
D/Wire ( 7664): http-outgoing-5 >> "Connection: Keep-Alive[\r][\n]"
D/Wire ( 7664): http-outgoing-5 >> "User-Agent: DAVdroid/0.8.0[\r][\n]"
D/Wire ( 7664): http-outgoing-5 >> "Authorization: <stripped>
D/Wire ( 7664): http-outgoing-5 >> "[\r][\n]"
D/Wire ( 7664): http-outgoing-5 >> "<C:calendar-query xmlns:C="urn:ietf:params:xml:ns:caldav" xmlns="DAV:">[\n]"
D/Wire ( 7664): http-outgoing-5 >> " <C:filter>[\n]"
D/Wire ( 7664): http-outgoing-5 >> " <C:comp-filter name="VCALENDAR">[\n]"
D/Wire ( 7664): http-outgoing-5 >> " <C:comp-filter name="VEVENT"/>[\n]"
D/Wire ( 7664): http-outgoing-5 >> " </C:comp-filter>[\n]"
D/Wire ( 7664): http-outgoing-5 >> " </C:filter>[\n]"
D/Wire ( 7664): http-outgoing-5 >> " <prop>[\n]"
D/Wire ( 7664): http-outgoing-5 >> " <getetag/>[\n]"
D/Wire ( 7664): http-outgoing-5 >> " </prop>[\n]"
D/Wire ( 7664): http-outgoing-5 >> "</C:calendar-query>"
E/ActivityManager( 1021): checkUser: useridlist=null, currentuser=0
E/ActivityManager( 1021): checkUser: useridlist=null, currentuser=0
E/ActivityManager( 1021): checkUser: useridlist=null, currentuser=0
E/ActivityManager( 1021): checkUser: useridlist=null, currentuser=0
E/Zygote ( 9516): MountEmulatedStorage()
E/Zygote ( 9516): v2
E/SELinux ( 9516): [DEBUG] get_category: variable seinfo: release sensitivity: NULL, cateogry: NULL
E/PhoneWindow(21526): Circular progress bar not located in current window decor
E/ActivityManager( 1021): checkUser: useridlist=null, currentuser=0
E/ActivityManager( 1021): checkUser: useridlist=null, currentuser=0
E/ActivityManager( 1021): checkUser: useridlist=null, currentuser=0
E/ActivityManager( 1021): checkUser: useridlist=null, currentuser=0
E/Zygote ( 9534): MountEmulatedStorage()
E/Zygote ( 9534): v2
E/SELinux ( 9534): [DEBUG] get_category: variable seinfo: platform sensitivity: NULL, cateogry: NULL
E/DownloadManager( 4736): SB enabled
E/DownloadManager( 4736): SB enabled
D/Wire ( 7664): http-outgoing-5 << "HTTP/1.1 404 Not Found[\r][\n]"
D/Wire ( 7664): http-outgoing-5 << "Date: Fri, 29 May 2015 14:46:45 GMT[\r][\n]"
D/Wire ( 7664): http-outgoing-5 << "Server: Apache[\r][\n]"
D/Wire ( 7664): http-outgoing-5 << "X-Frame-Options: SAMEORIGIN[\r][\n]"
D/Wire ( 7664): http-outgoing-5 << "Strict-Transport-Security: max-age=63072000; includeSubDomains[\r][\n]"
D/Wire ( 7664): http-outgoing-5 << "Transfer-Encoding: chunked[\r][\n]"
D/Wire ( 7664): http-outgoing-5 << "Content-Type: application/xml; charset=utf-8[\r][\n]"
D/Wire ( 7664): http-outgoing-5 << "[\r][\n]"
D/HttpClient( 7664): Connection can be kept alive indefinitely
D/HttpClient( 7664): Authentication succeeded
D/HttpClient( 7664): http-outgoing-5: Shutdown connection
D/HttpClient( 7664): Connection discarded
D/HttpClient( 7664): http-outgoing-5: Close connection
D/HttpClient( 7664): Connection released: [id: 5][route: HttpRoute[{s}->https://apps.kolabnow.com:443]][total kept alive: 0; route allocated: 0 of 2; total allocated: 0 of 3]
E/davdroid.DavSyncAdapter( 7664): Hard HTTP error 404
E/davdroid.DavSyncAdapter( 7664): at.bitfire.davdroid.webdav.NotFoundException: 404 Not Found
E/davdroid.DavSyncAdapter( 7664): at at.bitfire.davdroid.webdav.WebDavResource.checkResponse(WebDavResource.java:427)
E/davdroid.DavSyncAdapter( 7664): at at.bitfire.davdroid.webdav.WebDavResource.checkResponse(WebDavResource.java:405)
E/davdroid.DavSyncAdapter( 7664): at at.bitfire.davdroid.webdav.WebDavResource.report(WebDavResource.java:343)
E/davdroid.DavSyncAdapter( 7664): at at.bitfire.davdroid.resource.RemoteCollection.getMemberETags(RemoteCollection.java:100)
E/davdroid.DavSyncAdapter( 7664): at at.bitfire.davdroid.syncadapter.SyncManager.synchronize(SyncManager.java:78)
E/davdroid.DavSyncAdapter( 7664): at at.bitfire.davdroid.syncadapter.DavSyncAdapter.onPerformSync(DavSyncAdapter.java:146)
E/davdroid.DavSyncAdapter( 7664): at android.content.AbstractThreadedSyncAdapter$SyncThread.run(AbstractThreadedSyncAdapter.java:259)
I/davdroid.DavSyncAdapter( 7664): Sync complete for com.android.calendar
D/davdroid.DavSyncAdapter( 7664): Closing httpClient
D/HttpClient( 7664): Connection manager is shutting down
D/HttpClient( 7664): Connection manager shut down
Please let me know how to provide more/better information.