Strangely after being able to reproduce it most of the times I just had a hard time getting it to happen again right now.
OK, I tried the following now:
Reduce M203 Z to 600mm/min (and W always the same value set) -> I was unable to reproduce it with F601 (only a few attempts)
Increase M203 Z to 1501mm/min -> I was unable to reproduce it with F1502
After very many tries I was able to reproduce it again with M203 Z1500 and F1501
After homing W as at 0.3 and after it moved out of sync at the top it was at 0.0
AFAICT W stays at 0.3 after homing until I unhide the axis for the first time. If I unhide, hide, unhide it after homing without any movement it will switch it's position from 0.3 to 0.0
I saw it only once now that the left motor overshot
Reducing the acceleration from 100 to 75 made the overshoot worse, reducing to 50 made even "worser"
increasing the acceleration from 100 to 150 seemed to make it a bit better but still overshooting
Increasing acceleration further to 175, 200, 250 or 1000 (did not even know my Z axis was capable of that) I was not able to reproduce with or it was so low of an overshoot that it was no longer visible
EDIT: G92 W0 in homez.g seems to cure it.
