I've heard a video on Sweetwater's site that described the faders as noisy, but not jumpy. That reminds me of my old 01V96's faders before it died. It had a few channel faders that would get "stuck" between two values it was able to faithfully represent, and during a linear fade could jump between the two values erratically until it moved out of that spot. I recognized that as a failure state, where the fader itself was getting old and might not read correctly without a clean.
I also have a Faderport Classic, and I had to clean it after a spill early in the year, which I followed up with a "self test" i created to make the fader move as fast as possible from extreme to extreme, but also in steps, turning around mid-travel, and slowly up and down the length of the fader. If the points were too far apart to be reached and a new automation line started, the fader would try to jump to the new position, often quickly, so it would shake extremely hard. At first I was afraid I had completely ruined the track, but it didn't happen on slow automation.
So, I'm not sure what your specific issue could be, but I do believe that PreSonus needs to focus on what is good about their products and should actively be seeking to emphasize those aspects about it, instead of trying to go for this vertically-integrated, massive scale they've been trying to get to for the last decade. I think they have the capacity to be the best at what they are good at, including controllers like this, and are just not focused enough to be the best.
I hope if you can have PreSonus service the Faderport, even a paid service, that it comes back without jumping. It's a shame they told you that was normal operation.
