The issue is solved!
The 'enable x-y' was not touched and indeed disabled, but the phenomena did reoccur.
Somehow it did not work properly because the mouse was connected to a 3.0 USB-hub. When i connected it directly to the computer and did the reset as u described, i could change my DPI values without issues. (And after that it also work via the USB-hub again !?!)
Small sidenotes:
- The reset function in the top right corner ONLY resets the active profile, not the whole software!
- I can only enter DPI values with the slider. I could not find a way to make a value to 'stick', when entered with num-keypad....
Thank you for your swift support.