I had the same problem with my Thrustmaster Pedals. Erratic behavior all the time. The rudder was even moving without touching the pedals. Although the following configuration worked in principle , it sort of “disappeared” after I restarted FS 2020 and was back to its erratic behavior.
I then discovered a sort of work around that seems to work. After the sim has started and one has picked a location, a plane and the appropriate configurations in the options menue, the erratic behavior disappears once the plane is reloaded via the Developer Mode, which has to be switched on via Options/General. Then go to the appearing menu on top of screen and press Windows/Aircarft Selector:
and then pick the corresponding plane from the appearing list:
Now the pedal works as required with the mentioned configuration. I don’t know why, but it works…