MTH one scale that use larger motor have the rectifier heat sunk. In addition, when they used PS-32 board they added brass heat sink to the motor fets. PS-3 boards do a have a temp thermistor sensor that will kill power if temp gets too high and it is possible the Flash code may have a temp setting.
A lot of info to read above. Are you saying this worked fine since 2019 and just started to act up? If the engine stop but lights and sounds remain on, and you have control which I think you said you do, then the board still has power and I believe the motor fets are overheating, or some component related to motor operating. That is shutting down the motor and you get the abrupt stop. G
