Okay, the jurney go further.
I installed a container on ZimaOS (formerly CasaOS) with Homeassistant. After i plugged in my serial gateway to the computer and route the virtual serial port to the container, i could setup myssensors. And all sensors worked so far. But in the meantime ocasionally one sensor value stopped reporting, another value from the same sensor still works. Same behavor as in HASSOS on the RPI3.
I think i'm done with the serial gateway. Next step is to build a MQTT gateway. If this fails, i had to replace all mysensors devices :-(