#578 is caused by https://github.com/owncloud/contacts/issues/581 which is present since at least OwnCloud 6.0.3.
Please follow up in the issues mentioned above.
I am using acalendar+ and moved from caldav-sync to davdroid. Everythings works, I see my calendar and task entries from owncloud. But if I create a new task in acalendar+ and press synchronize (yes I prefer manual synchronizing), only calendar entries are synced. Tasks are only synced if I press “synchronize tasks” in the account settings menu or in the OpenTask App. With caldav-sync syncing of tasks directly in acalendar+ works, why not with davdroid?
Please ask aCalendar+ support directly.
… and please keep us up-to-date about what you have received
What ever happened with aCalendar’s Tasks module here?