Not sure though how “hasVCard4” works or what it checks…
I also could not find a reference logcat (to check against Radicales response)
But here is the relevant verbose logcat output:
[syncadapter.SyncManager] Preparing synchronization
[syncadapter.SyncManager] Querying server capabilities
[syncadapter.ContactsSyncManager] Contact group method: CATEGORIES
[HttpClient] --> PROPFIND https://dav.example.net/mail%40example.net/COLLECTION-ID/
[HttpClient] Content-Type: application/xml; charset=utf-8
[HttpClient] Content-Length: 296
[HttpClient] Depth: 0
[HttpClient]
[HttpClient] <?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 /><supported-report-set /><n0:getctag xmlns:n0="http://calendarserver.org/ns/" /><sync-token /></prop></propfind>
[HttpClient] --> END PROPFIND (296-byte body)
[HttpClient] <-- 207 Unknown https://dav.example.net/mail%40example.net/COLLECTION-ID/ (465ms)
[HttpClient] Date: Wed, 10 Oct 2018 09:44:01 GMT
[HttpClient] Server: Apache
[HttpClient] DAV: 1, 2, 3, calendar-access, addressbook, extended-mkcol
[HttpClient] Keep-Alive: timeout=5, max=100
[HttpClient] Connection: Keep-Alive
[HttpClient] Content-Type: text/xml; charset=utf-8
[HttpClient]
[HttpClient] <?xml version='1.0' encoding='utf-8'?>
<multistatus xmlns="DAV:" xmlns:CR="urn:ietf:params:xml:ns:carddav" xmlns:CS="http://calendarserver.org/ns/"><response><href>/mail%40example.net/COLLECTION-ID/</href><propstat><prop><supported-report-set><supported-report><report><expand-property /></report></supported-report><supported-report><report><principal-search-property-set /></report></supported-report><supported-report><report><principal-property-search /></report></supported-report><supported-report><report><sync-collection /></report></supported-report><supported-report><report><CR:addressbook-multiget /></report></supported-report><supported-report><report><CR:addressbook-query /></report></supported-report></supported-report-set><CS:getctag>"56fc12a79e549c5d6a97381653c7c0be"</CS:getctag><sync-token>http://radicale.org/ns/sync/REDACTED-TOKEN</sync-token></prop><status>HTTP/1.1 200 OK</status></propstat><propstat><prop><CR:supported-address-data /></prop><status>HTTP/1.1 404 Not Found</status></propstat></response></multistatus>
[HttpClient] <-- END HTTP (1086-byte body)
[syncadapter.ContactsSyncManager] Server supports vCard/4: false
[syncadapter.ContactsSyncManager] Server supports Collection Sync: true