This is not related to updating Android. Please follow up at https://forums.bitfire.at/topic/1259/rev-must-not-appear-more-than-once-in-a-vcard-component/
So I have been using Davdroid for a while now and it has been working seamlessly with Nextcloud. Yesterday I upgraded my phone rom Android 7.0 and restored Davdroid from a Titanium backup I made before the upgrade.
The first bit of strangeness was that the account data was not restored. Hmm. ok no big deal I just re-add my account and let it sync with the server again. Only it did not work out that way. I put in the credentials and I press login and it just sits there.
On the server nothing has changed and you can see from the logs it connected before and 4 hours later would not connect (after my rom upgrade)
For the record.
Nextcloud v 12.0
I have to end up killing DAVdroid because it never times out.
Can you provide adb logs? Just run
adb logcat. Sounds like a connectivity problem – every request will time out but there are a lot of requests involved in the detection process, so this can take very long.
Actually it seems to correct itself after a reboot? Hmmm. Odd.