I’ve gotten a few (well, more than a few) electronic typing machines into the shop that when tested do weird things. One machine would not return when the return key was pressed. Another would tab intermittently. The last didn’t like its back space key pressed. Maddening things. Mostly prevented by keeping the typewriter clean and covered when not used.
Here is a photo of a circuit board that had intermittent shorts across terminals from copious lint and dust. This was causing the problem and once the debris was removed and the board cleaned, the typewriter behaved like Billy (nice and well behaved). Be like Billy!
Keep your typewriters clean and they will serve you well.