I wanted to answer this in the hope it would help.

As Radoslav pointed out, what it did come down to was "something completely unrelated is using the same multicast IP/port". As it turns out something else on the network was using this port and somehow getting into jgroups processing causing the strange version to appear and mismatch in the packets. It was unfortunate because it did give off the impression that there was something wrong from a configuration standpoint i.e. The version imported to the jar was mismatching.

Switching to a completely unused port on the machine allowed this to work first time.

Hope it helps if someone else faces this in future.