Hey @SupportiveEntity! Thank you very much for your answer 
The constraint is setup appropriately. All the linar limits are locked.
Twist and Swing1 also. Swing2 alowes 80 degrees to let the lever go up and down.
I grab the lever also with a constraint.
To controlling the stiffines I use the angular motor with the drive mode twist and swing and using swing. The target velocity is set to euler 0, 0, 0 with the strength 500.
This simple example works perfecly fine in 4.27.2 and are broken in 5.3.2.