Your implying the last problem was solved. It never was.
It sounds like a harmonic type issue. I’m sure there are feedback circuits that make changes to torque at certain rates. Perhaps at the rate of vibrations (or some multiple) under low accel. Could be feedback loops are perfectly out of sync between the front and rear drive. Those feedback loops are probably in a complete different mode (update rate) under hard acceleration.
It could also be a harmonic between these feedback loops and the motor mounts.
Too bad there is no Track mode so you could play with bias.
I wonder if you could trick it to disable the front or rear drive unit. Just to test it.
Changing heights etc. changes the harmonics.