I had an older PS1 loco that would do the same things on my MTH z1000 transformer.
I put the same train on my test track with a much older Lionel TW 175 Train Master and the unit worked 100%.
I was told it has something to do with the Quasi Board or the algorythms or something like that.
Pretty weird that an MTH train does not work on a MTH transformer.
That was the only time I had that issue.