I had a similar issue, and it was because my joystick deadzone in SteamOS’s settings was too low. The joystick registering an input changed the functionality of those two buttons, registering as a different hotkey/shortcut. It’s possible one of your other buttons is stuck, but it might be difficult to figure out which one.

Whenever I’ve had a button go unresponsive, most recently the power button, I dip a q-tip in rubbing alcohol and wipe it around the button and let it soak into the gap. No need to disassemble. I do it three times and let it dry completely and then they go back to normal. I’d try that first before disassembling or starting a steam support ticket.