However, years on the electronics workbench just makes one expect the unexpected. So, cleaning/re-seating contacts is a first and certainly cheap step.
In the early days of video arcade M/Cs the program was held in anything up to 30 EPROMS all plugged into sckts on the mother board. Just slipping a screwdriver under each end of each of them and lifting them a bit and reseating them would cure most faults.