Hey @FrankR,
thanks for testing again! I’ve followed along your description and found an error in openHABian! 
After another recent change there was one dot missing 
Fix typo in serial port function sed line · openhab/openhabian@308a39f · GitHub
The whole process will work for the next user now. Your help in resolving this matter is really appreciated! Best Regards and let me know if you encounter any other issue.
Btw. did you see the openHABian v1.3 announcement?