lol after posting and posting I got with a new built 22 to the track and had exactly the same problem. New kit, midmotor. Than I checked my rear motor 22 and the slipper is much softer but ok.
So you are not alone any longer
I will try the associated slipper clutch and let you know.
edit: Seems to be the slipper pads, I tried the team C spring which is even a bit stiffer and still have the problem.