perplexing, indeed.
I think verifying proper power and power master operation with a light bulb, lighted car or a voltage meter will help you find the issue.
test power master operation viewing voltage up down changes, take track voltage readings approaching the cross area and the cross area and see what you find.
The MTH engines could be more sensitive to a track power condition that regular conventional engines. But, you need to start somewhere to rule out variables.
Good luck.