I think that the mechanism that opens the lens has worn down over time. There are no sensors that I know of which can detect the camera's orientation, so my best guess is that the connection that turns on the camera is loose and only becomes active in certain angles. If possible, you should take it apart using an online guide for your camera and make sure all the connections are tight.
I actually found a relatively simple solution for this problem. Turns out, when I reassembled the controller after cleaning it, I did not put the little screw on the motherboard tight enough. This caused the little pins on the membrane that connect to the motherboard to be slightly misaligned. Tightening the screw seems to have done the job!
