Failover scenarios are currently not supported. Not supported means that some scenarios might work, and some others don't. As an example, failover works for hardware endpoints. This will be fixed in the next major release, X.14, but might require an ...
To troubleshoot, go on Expressway->Status->Unified Communications status. If something is broken it would show up on Expressway-C.
Other tool is the Collaboration Analyzer https://cway.cisco.com/csa/ which simulates a Jabber login. You can find some ...
Yes, diagnostic logs can help. Issues might be different, from DNS to SSH tunnel between Expressway-C and Expressway-E. Go to Maintenance->Diagnostics->Diagnostic Logging->Start new log and then login with Jabber
