It could be a CPU or subtle issue with power. But as I see the test mode I notice the bottom opto (off cam) is not changing.
Look at your video. The two little nubs under the graphic of the time expander represent the opto emitter/receiver on the bottom of the MPF.
There should be a beam (straight line) between the two that signals a beam is present or broken.
Check the optos to make sure they are working.