@walter-schilder We are currently working on it. It will probably be contained in the next version.
Custom events will be synced as X-ABDATE, like Apple (and some compatible systems like Synology) does.
After editing two contacts in Nextcloud 13.0.2 hosted on a Debian derivative, I tried to sync back to my Android device running DAVdroid 1.11-ose downloaded from F-Droid. The result was that all contacts on the device (Samsung Note 3 running Android 5.x) were removed, even from all other accounts (Device, Google, Telegram, SIM, and Nextcloud). The data remains on the Nextcloud server.
Here is the debug log:
I’m happy to help to reproduce the bug and triage solutions as need be.
Should be fixed with 1.11.1-ose. Can you confirm this?