According to the logs:
EXCEPTION java.io.IOException: stream was reset: REFUSED_STREAM
this is a duplicate of nginx HTTP/2 incompatible with okhttp. Please follow up there.
until yesterday I used Owncloud 8.0.x and Contacts for synchronization of my contacts with DAVDroid on my Samsung Smartphone. No problems with that.
Yesterday I upgraded Owncloud to 8.1.1 with Contacts+. I imported my contacts from Contacts to Contacts+ without any problems. But no I can’t syncronize my contacts with the corresponding CardDAV link. DAVDroid endless requests the server informations after I have given all credentials.
Calendar+ works fine with DAVDroid.
Has anyone an idea?