Problem solved by changing the following things:
1.) Switched the Source Extraction Method for my Local Astrometry solver to Builtin method for solver.
2.) Instead of taking RAW images with my Canon camera for polar alignment I took Medium Fine JPEGs.

Still don't understand why, but using the above settings I have no more force close of KSTARS v3.5.5 on polar alignment.
Maybe this helps also others.