I agree that this looks like a server side issue on the IG. I started seeing this behaviour at the end of August.
My java code is unsubscribing and disconnecting from lightstreamer and from my log-files this is successful.
I have put a retry around the lightstreamer openConnection method and wait for 30 secs.
The issue is easily reproducible and I can see successful connections after a couple of attempts with the modified code.
I suggest that IG fixes this rather than assuming users are breaching session limits. In my case I am definitely running one Java jar file that connects on a single thread for the api key I am using.