I just tried the medicine, but it has no effect. While thinking about the issue it is like a one way sync but without davdroid reading the entries on the server. My girlfriend actually has the exact same phone with an older android version i will install davdroid there and see if it shows the same behavior.
Crash after Android update 7 -> 8
I updated my Note 8 from Android 7.0 to 8.0 today and now as I open the DAVdroid app it is simply crashing right on the startup. Any solution to get it working again?
Please have a look at https://www.davdroid.com/faq/davdroid-not-working-after-update/
Have you tried to uninstall DAVdroid and then install it again?