I, too, am working through configuration issues with Rocket.Chat. I really like the LDAP integration with UCS, etc. I am immensely frustrated with the mobile notification / push problems. It simply does not work as installed from UCS.
Web client to web client seems good. Web client to mobile rocket.chat or mobile to mobile works as a chat app fine, just as long as the user is online and active. Otherwise, no notifications and the user drops offline.
On other systems, I have been using XMPP client xabber app logged into XMPP servers Prosody and Openfire. Notification to the mobile android app are stable and work well. I was hoping to use the preconfigured rocket.chat as a complete solution, but, the lack of mobile notification is a real problem.