Maybe a bad solder joint for board-mounted part of the connector??? Wiggle things. Maybe it will quit again.
Almost 40 years ago I built a computer as a hobby project. It ran the PDP-8 instruction set. The only reasonably-priced core memory stack I found was surplus from an IBM-1620. When unsoldering the remains of the cables which had been cut, I discovered that three of the wires were just stuck in terminals and had never been soldered. It became obvious why the unit had reached the surplus market
