Manual cars coming out of gear

Help me, I don't know what is going on. Whenever I drive a car with a manual gearbox the drive will disconnect at random, for no apparent reason. Like the clutch is depressed. This happens both with realistic and arcade shifter mode.

The only way to re-engage the drive is pressing the mapped clutch key. Then it drives normally again for a 20-30 seconds until it comes out of gear again.

Very annoying!
--- Post updated ---
I added the pedals ui element and when this happens the clutch input gets stuck at 79. If I press shift it goes back to zero.

 

I figured it out, there was a phantom axis mapped to the clutch, after removing it the issue is fixed.