I've been using DAVDROID for many years. I sync it with NextCloud (previously OwnCloud), and have been doing that for years too.
Recently I configured a new phone (Samsung Galaxy A5 2017). I set DAVDroid up as per normal.
I found, however, that a considerable number of contacts were not displaying correctly. They would come up with an almost entirely blank page, with just one detail like perhaps a phone number. No name, no photo, no other details. Just blank. There is no EDIT menu, and the three dots menu only has "Block number" showing. None of the other options show up (like Delete, Manage linked contacts, Mark as default, etc).
I figured it might be an issue with the Samsung Contacts app. I found I can view those troublesome contacts in other contact apps. This seemed to prove my assumption.
But then I ran a test, by installing CardDav-sync app. When I view the same contacts (those that won't display) via the record created by CardDav-Sync, it displays in Samsung Contacts normally, and can be edited, etc.
So the issue appears to be DAVDroid (DD) related.
I have removed the account from DD, and set it up again. The issue persists.
I also updated NextCloud from 11.0.3 to 11.0.4. No change.
Any suggestions on how I might get aa DD contacts to function properly again?
UPDATE: Since removing and reconfiguring the account in DAVDroid, the contacts with issues don't work when viewing from CardDav-Sync either. Previously they worked from there when I tested it.