Try unplugging the opto card on both sides and resetting the plugs there. Could also be an alignment issue on the optos in the jam positions so that the light beam is not directed properly. Make sure that there is nothing blocking the light beam between those 2 optos, like being dirty, or some other obstruction that might simulate a ball stuck in the jam position. Try placing something in the light path while the optos are active to see if they react on the trough test. If those things don't correct the issue, you might need new opto boards or new optos to install on the existing cards.

I think these are the correct transmitter and receiver cards here if you decide that you need some new ones.
Check the part numbers to make sure, if you decide to get some.
https://www.pinballlife.com/stern-spike-trough-serial-opto-transmitter-board.html
https://www.pinballlife.com/mm5/merchant.mvc?Screen=PROD&Product_Code=520-1051-00
You can also replace just the optos on the cards, if nothing else is wrong.

They do go out. The trough opto cards on my machine also needed to be replaced, but my machine is a different Stern model, requiring different opto cards.