So I found out that the GP38 has a problem with its banking comm. So, I started a service with banking locos, set up the loco as usual, activated banking comm as usual. I started accelerating and checked whether the banking locos are doing their job by switching camera to them. They properly did their work. After about 10-15 minutes in the services and arriving at a steeper gradient, I feel that somehow I suffer a lack of power for a 3kt trains powered with 3 leading locos and 2 bankers. So I switched the cam back to the banking locos and guess what: they were idling. So I put throttle into off, reverser into neutral and right at the point where I clicked on the banking comm button, the game crashed with an Unreal Engine 4 Error Stack Overflow. It is kind of reproducable since I had that one several times after doing the exact same steps to reactivating the banking comm on the GP 38.
