Software Upgrade : LTM stopped working

It sounds weird, but here's what you should try to diagnose the issue.You should run tcpdump, enable the configuration to log causes of RST sent by LTM, and if you have ssl based profiles, you would also need to reduce the cipher strength to NONE. Did you also go through the release notes, it's obvious that the current scenario you are in, won't have been predicted, but yes, there are few things they recommend which come into play. Please raise a TAC case as well.