I have an old laptop I use as a server, it sits on top of a cabinet in the corner of my room. One day I noticed it seemed like the space key was being held down all the time, but only past the login screen. I was about to buy a new laptop because I thought the keyboard was totally broken (and its kind of old anyway). Turns out an old Bluetooth keyboard in my closet that was paired to my laptop got switched on at some point and the space bar was being pressed.