Event changes are not saved

Hello!

I've got 2 caldav GMX calendars synced and use thundebrird on my Windows PC and everything works fine.

The only curios thing is sometimes, when I change the time of an appointment, or thr color or delete it or something in the android app it isn't saved. I mean all locally in the android OneCal App. I edit the event, I press the save button. And in the overviee of the month the color change didn't work.

This only happens sometimes and I can't find a pattern to it. Also there is no sync animation or anything that would indicate the issue would stem from synchronization. At least from what I can tell. Pressing the sync button hasn't helped either.

This occurs around 10% of times that I edit an appointment, I estimate.