DAVDroid has recently begun to duplicated repeating events [annot: just checked: This does not only affect repeating but also one time events, not all of them, though] from two of my calendars, both of which are from Nextcloud 11. One of the calendars being readonly, the other one read-write. I see one event 8 times for the same date, another one 4 and another one 2 times. I have no issues with them on other clients.
I used to observe the same problem in the past, but at some point it went away. Now it is back, for some reason.
If you need logs, I can happily provide both DAVdroid and nextcloud server logs, but I am not sure what kind of logs are needed, please advise.
My phone is running an unofficial version of CM 12.1, Android 5.1.1