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.
Dear DAVdroid team,
with all my SOGo instances (I have four in differing versions and setups for different organisations) using DAVdroid failed to show up any calendars and address books. This could be reliable tracked down to “subscriptions” of other users’ calendars: As soon as a single calendar of another user is subscribed to in the SOGo web interface, DAVdroid would fail to load / refresh both the lists - even if it had successfully done so before subscribing.
This comes down to the following request from davdroid to SOGo:
which sogo routinely answers with a 403, and DAVdroid stops with error.
The (for me) easiest workaround was to add a RewriteRule to my Apache:
RewriteRule ^/SOGo/dav/([a-z0-9@_.-]*)/calendar-proxy-write/?$ /SOGo/dav/$1/ [L,R=301]
Now DAVdroid works.
I am not sure if DAVdroid should not ideally ignore the 403 (as calendar-proxy-write is not in use unless delegations are, right?). As this is a problem only in autodetect, I guess skipping the 403 might do the trick.