I’m getting the same behavior. Really started ramping up over the past few days. I get a “Credentials needed” warning in Android (using ActiveSync). When I hit the “Done” button to accept, I get a “Validating server settings” popup window that oftentimes fails with “Couldn’t finish Can’t connect to server”. IMAP access seems to work fine on a Linux system while this is going on.
I’m poking around the logs to see if there is anything obvious.
Looks like backend authentication to CardDAV is failing: BackendCardDAV->Logon(): User ‘xxxx’ failed to authenticate on ‘https://127.0.0.1:443/carddav/addressbooks/xxxx/’:
this and other errors repeat in the log
web backend might be down: Exception: (Exception) - Woops, something’s gone wrong! The CardDAV server returned the http status code 504.
lots of timeout errors: xxxx upstream timed out (110: Connection timed out) while reading response header from upstream, client: 127.0.0.1, xxxx…
see a critical error as well
connect() to unix:/var/run/php/php7.0-fpm.sock failed (2: No such file or directory) while connecting to upstream, client:
this one seems tied to access from the Android client