[Jamming] Booklet Finisher SD-534 paper jam at saddle stitcher

[mgasperl]

Hi,
after working fine for months no paper passes the saddle stitcher; it curls there. Jam location: 36, no jam code displayed.
I attached 2 photos of the spot.
IMG_20200203_011423_072.jpgIMG_20200203_011420_150.jpg
Printer: KM C308

I already removed loose clambs on all three stitchers and did a cleaning. Do you have ideas how to solve this problem?
Best, Mike