Surface Book 3 keyboard backlight no longer works, solution?

HelloI have a problem with my keyboard on the Surface Book 3. The backlight no longer works, although it worked perfectly at first. For some time now, the backlight has suddenly gone out. Interestingly, however, the lightning of the Caps Lock key, the Fn key and the detach display key continue to work. So only the full backlight seems to be affected. The associated F1 key works fine, but it no longer activates the backlight. I have already tried the Surface Diagnostic Toolkit and resetting the device, but have not found a solution.Have any of you had the same problem and were you able to solve