Pressure dropping

Hello

I have recently rebuilt my rig, and after putting everything together, i am having trouble with my fanatec pedals (CSL Elite LC).

I had trouble getting use to the new way i was sitting on the rig and after a few days of mssing with settings, calibration, etc, i noticed that when i physically keep the pressure contstant, it looks like the input drops, even though i don't lift the foot off the pedal.

Is this a known syptom of some deffect or some other problem that i maybe have stumbled uppon? Innitila presssure seems to register ok, but gradually drops after that. What could this be?