The CDM uninstaller I already tried, but it didn’t help. I performed some more investigation and found the cause of the problem. The information might be useful for others as well.
For some (FTDI based) embedded debug tools I had a (libkUSB) driver installed using Zadig (https://zadig.akeo.ie/)
This driver captured the 2nd serial converter of the SA124B. After uninstalling this driver the SA124B/TG124A worked flawlessly.
Thanks for your support.