I am currently rebuilding my ownCloud server, so the DAV endpoint currently return a 403 Forbidden error. The following is observed with DAVDroid 1.3-ose from F-Droid on a CM13 device.
DAVDroid doesn’t handle this very well: every few minutes, it spams my notifications with errors. The number seems to match the number of collections configured to be synced.
Even if I swipe them away, they come back pretty soon, after what I assume is the sync period.
It might be better to only show one aggregate notification (which I think was the case in the past), saying something like “Some synchronisation tasks failed”, and offer the full list when the user taps the notification.