Why is my Steam Deck scrolling down automatically?

When I booted up my Steam Deck after a period of not using it, it loads to the main menu but then starts scrolling down automatically until it hits the bottom, and then the "end of menu" pinging starts repeatedly sounding. I can move up using the left control stick and then move around menus normally, but then seemingly at random times, it starts scrolling down again.

When I go to Test Device Input, the buttons that don't respond/light up on the diagram are the D-pad (all directions), the View button (the one right next to the D-pad), Y, and B buttons. The Steam and Quick Access buttons do light up, however as soon as I press either button, the device backs out of the input test as if it were a long B press and then the auto-scroll down issue starts again.