In case the following information helps for your reference, I've had some of the clone 6-button controllers sent my way to repair in the past, generally the fault lay in the ribbon cable bridging the two PCBs having a few broken wires where it's soldered in, but I did find the following in my notes:
My suggestion if you can't find obvious breaks in traces or no failed continuity in the controller cable is to replace both 74HC04D and 74HC14D with Toshiba branded ICs, the manufacturer probably went with generic knockoffs that would be less reliable.
Edited in note: Manufacturer in this context would be the overseas factory that assembled those controllers for Starwander, not Starwander himself.