I've seen that before, but I couldn't confirm anything in particular was causing this.
I'm not sure if this will help but if you are playing this session after bringing the route in from TRS19, I recommend opening the route, move a tree or something slightly enough to force a save and then save the route so it's updated to the current TRS22 build and the repeat that in your session by moving a train slightly to force a save.
I have found this helps with my routes and sessions, like anything Trainz it may or may not work for you.