As the problem also appears with direct access via curl and only in the original account (and not in the newly created test account), I guess that it’s not a DAVdroid problem. I’ll close the issue – if you find any hints that it might be a DAVdroid problem, please post here and I’ll re-open.
Tasks only caldav doesn’t sync
I created a tasks list in nextcloud application but it doesn’t appear in davdroid after sync.
I don’t have problem with a classic calendar with task list.
You need to install Open Tasks to be able to see tasks on your Android phone. Please be sure to install Open Tasks before installing DAVdroid. You may need to uninstall DAVdroid, install Open Tasks and install DAVdroid again.
Ok, forget my question, that works fine when I sync caldav only.