Found a solution. Apparently a couple of index cards had fed through far enough into the machine to be impossible to see. Anyone else running into this issue might like to try the location at https://community.usa.canon.com/t5/Printer-Multifunction-S...
Hi Patrick, I have this same issue. Apparently it seems quite common, but there's an issue with your advice. If having ensured that the paper jam (if there ever was one) has been cleared we are to follow the steps in the second link, but if that fail...