Probably all contacts which are edited otherwise are working. You can also edit a contact with photo in the Posteo Web interface and then Posteo will send the correct photo, which can then be synchronized.
Due date in task
I know an unpleasant problem. If I create a task in my calendar and sync with my nextcloud server, I have the dates included. If I access to this task from Qownnotes the dates do not appear. I exchanged with Qownnotes developer and we do not understand why the date disappears. Which paterns are used to synchronize tasks in davdroid ?
Please provide steps to reproduce (including Web and application server logs), DAVdroid debug info, verbose DAVdroid logs etc.. I don’t even know what Qownnotes is.
Seems to be a 3rd-party problem, see https://github.com/pbek/QOwnNotes/issues/664