As to add to the above topic; mostly for public reference. I am running into the same problem where indeed a switch of network (WiFi > 3g/4g > internal/external) leads to this situation; a full reset of the jabber client with renewed authentication resolves the issue for the moment but is deemed very inefficient.
The above suggestion did not correct this matter for me however; accordingly i'm still in search for a solution.
CUCM 10.5.2 combined with WebEx IM (Instant Messaging)
Jabber Clients: Jabber for iOS & Android 11.7
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