This still seems to be an issue (at least I have the same problem, with Nextcloud).
Where can I find #219?
The issue tracker on the Gitlab project seems to be disabled.
for DAVDroid 1.3.4-1-ose on Androdi 6.0.1, on first launch DAVDroid fails with exception of there are existing entries in the calendar.
When those calendar entries are copied to the server DAVDdroid experiences a Java Excveption and synchornization fails
To be able to use DAVDroid, all existing calendar entries must be removed