Marvin,
I solved the deadlock issue by putting a queue in front of Station3 (it had a much longer process time than any of the other stations). as station3 takes much longer to process, I tried to create two replica Station3's, feeding from a single queue and then back into another single queue, which then connects to the robot. Only now the deadlock issue re-appeared! It was Station2 which was being blocked for some reason so I put a queue in front of that one, and now it seems to work!
Rabi