Okay, thanks for clarifying your non-use of mpi4py. That means the finger is pointed at ParaView itself.
Looking at the coprocessing python module, as best I can tell your backtrace involves the call here. Now, the question is, where are the other MPI processes stuck? If it is possible to get a stack trace on one of those processes, then we can see where things go awry. I know that isn’t the easiest or quickest thing to do, but without that, finding the communications mismatch is a bit like a needle in a haystack.