Success!!
I finally was able to fix this problem.
The problem was caused by the stepper timing settings
The following settings are working without Z-shift:
MINIMUM_STEPPER_PULSE_NS 3000
MINIMUM_STEPPER_PRE_DIR_DELAY + POST_DIR_DELAY 30000
The DIR_DELAY is now 6 times longer than it usually has to be with this motor, I have no idea why. According to the manual, it only needs 5000 ns.
However, this fix works for me, finally !!!
Since the MINIMUM_STEPPER_PULSE time is the same as before, I can still print with full speed. The additional DIR_DELAY only costs a few extra seconds for every print hour, depending on the geometry.
While this is not great, it´s at least usable. Maybe the developers can find out what´s the reason for this strange behavior sooner or later.
I still think that there is something messed up with the motion or path planner in Marlin: The problem only appeared when the Z-move was followed by an XY-move, while a pure Z-move without XY didn´t trigger the Z-shift. This means it can´t be related to the motor.
I´m currently printing the failed 24h-print again to check if the problem also disappears under real conditions, but I am very confident.
I finally was able to fix this problem.
The problem was caused by the stepper timing settings
The following settings are working without Z-shift:
MINIMUM_STEPPER_PULSE_NS 3000
MINIMUM_STEPPER_PRE_DIR_DELAY + POST_DIR_DELAY 30000
The DIR_DELAY is now 6 times longer than it usually has to be with this motor, I have no idea why. According to the manual, it only needs 5000 ns.
However, this fix works for me, finally !!!
Since the MINIMUM_STEPPER_PULSE time is the same as before, I can still print with full speed. The additional DIR_DELAY only costs a few extra seconds for every print hour, depending on the geometry.
While this is not great, it´s at least usable. Maybe the developers can find out what´s the reason for this strange behavior sooner or later.
I still think that there is something messed up with the motion or path planner in Marlin: The problem only appeared when the Z-move was followed by an XY-move, while a pure Z-move without XY didn´t trigger the Z-shift. This means it can´t be related to the motor.
I´m currently printing the failed 24h-print again to check if the problem also disappears under real conditions, but I am very confident.