I have the same case that SFOS cannot connect to ejabberd after upgrade to SF 4.0.x. Through all SF upgrade cycles from 1.x to 3.x XMPP worked fine. After upgrade to 4.0.x I only see these errors in ejabberd log:
Failed to secure c2s connection: TLS failed: SSL_do_handshake failed: error:somenumber:SSL routines:tls_early_post_process_client_hello:unsupported protocol
Thought that I’d try your workaround.
But how did you manage to to “pkcon remove telepathy-gabble”? In my case (running as root) it ends up with Fatal error: this request will destroy your system (my free transaltion).