Bingo, after I have disabled the feature section, I got control over the OnStep STM32F303 controller.
Thanks for this hint.
I have to find another solution for my DEW Point heater. Something must be changed within Ekos or KStars that this happend. The systems runs quite stable without any failure before I updated kstars with Astroberry.
I'm planning to switch to MaxESPV3 controller where I can control a field-rotator with the second Focus stepper. The PCB is already fully equipped for testing. The Advantage of STM32 is the very low power consumption in comparison to MaxESPV3.
Thanks again James