I will answer based on your description:
# It could be decoder (clean your printer decoder) located on the left side (round plastic materials) when you head face to face with the printer.
# Also it could cause by ( i'am sorry to say) defect of the optocoupler/decoder censor(tiny black square that read the decoder).
# Firmware issues/e-prom about to short
When the problem still occur please put a video above or below my answer to make me understand better where is the faulty.
Hope this will answer your questions.