Yeah, that’s not right. I’m pretty sure AT should be able to fully open the filter (or any parameter it modulates). Maxxing out the modulation in the setup menu and only getting the slightest effect when applying pressure certainly isn’t right.
As for repairing it. If you feel confident about opening it up, someone already said you could check the ribbon cables.
Check if the bigger ribbon cable in the middle underneath the keybed is seated properly and check the smller one with the blue connector. Sometimes ribbon cables get dislodged when a synth/keyboard is moved around.
Here’s a thread that will come in handy: