Since I much prefer to drive my engines myself and only use AI to occasionally move a train of wagons from one place to another while I'm busy with something else, so if the 'dumb dog pees on the carpet' my reaction is to shoot it dead and bury it. I can't be bothered with mucking around for hours second guessing what the robot drivers are going to do next.
I have "fired" more than one AI driver in my Trainz lifetime. Unfortunately after their termination, the labor board ruled in their favor as it was found out their errors were my doings.
I had one session setup where a driver kept going back and forth between stops, but looking at the schedule showed nothing out of the norm. I fired the driver and hired a new one and the new guy fell off the footplate as well and got the boot. After checking again, I found I had put down the same track mark in a row among a bunch of other track marks, which made seeing the redundant one almost impossible to find.