Take it for what it's worth, I'm no electronics guy, but I do understand electron plumbing a bit.

I'd be looking for a cold or failed solder joint on the memory slot a/o MoBo slot connectors.

Most likely I'd just reflow all the joints on the side of the memory card that needs pressure applied to it.

test

Re-flow the other side if the fault persists.

test

Re-flow the joints on the side of the MoBo Connector if it's still borked

test

Ditto the other side.

test

Scratch my head and wonder where I can find another Memory Card to test.

Do the last thing first, maybe you'll find one to borrow, they're in a bit of demand, or were . . . :-/