Best guess without looking thru the many BBSHD threads for similar issues is that there is a (PAS) sensor failure inside the BBSHD casing. Could be the sensor itself, or a connection issue.
Many connection issues are either wire damage at the exit/entrance to/from a casing or a connector, or water intrusion into contacts or wiring, so those are something to check.
Another possibility is random settings corruption; unfortunately semiconductors are vulnerable to this kind of thing from various sources. You could note down all your settings, then reset to factory defaults, and see if it changes the behavior. If it works correctly (for factory settings) then begin putting your own back in and retesting at each step to see if any specific setting changes behavior to incorrect operation.
It can also be firmware that has become corrupted; I don't know that there is a way to be sure of getting the correct / same firmware for your unit to reflash, and the wrong firmware can brick the controller. Even if it's correct for your controller version, it may change it's behavior from what you're used to. There are some threads with various firmwares in them, and discussion about them.