For me the same problem was resolved with disabled authentication in ZM options (uncheck OPT_USE_AUTH).
The reason to make this conclusion is here in logs:
===================
Aug 19 00:21:00 ubuntu-server zms[5623]: ERR [Unable to authenticate user]
...
Aug 19 00:21:00 ubuntu-server zms[5633]: ERR [Unable to authenticate user]
Aug 19 00:21:10 ubuntu-server web_php[5446]: ERR [socket_sendto( /tmp/zm/zms-289356s.sock ) failed: No such file or directory]
===================
For me the same problem was resolved with disabled authentication in ZM options (uncheck OPT_USE_AUTH).
The reason to make this conclusion is here in logs: zms-289356s. sock ) failed: No such file or directory]
===================
Aug 19 00:21:00 ubuntu-server zms[5623]: ERR [Unable to authenticate user]
...
Aug 19 00:21:00 ubuntu-server zms[5633]: ERR [Unable to authenticate user]
Aug 19 00:21:10 ubuntu-server web_php[5446]: ERR [socket_sendto( /tmp/zm/
===================