Main level knob no function

The knob for Main Level has suddenly stopped working. When I turn it I can see that the blue level indicators get stronger, but it doesn't affect the actual volume. The S4 MK2 is selected in the Traktor Manager Editor, all other hardware buttons and controls are working perfect. I noticed that the Assignment Table field is completely empty. When I open the NI Controller Editor, I can edit every control element except the Main Level, there is no CC controller value.

I tried to import a default TSI file for the S4 MK2, but couldn't find one on my hard disk.

Thank you for any help