I have a similar issue like reported in this issue: https://forums.bitfire.at/topic/1843/davdroid-stops-syncing-without-throwing-an-error
Since a while I don’t recieve event updates anymore. The sync is started regularly like before, but the log doesn’t show any activity of an actual sync.
I.e. I create an event in the calendar but it doesn’t get synced to the server (nextcloud). Same of all of my accounts (including owncloud). I can confirm the server has not been updated in a long time (2y).
Everything worked fine a few weeks before.
Attached is the sync log.0_1538644505665_davdroid-25831-20181004-102417.txt