Face buttons sometimes don't work (ABXY)

I'm posting this here as a possible solution to buttons not working or being temperamental

Issue: Face buttons sometimes fail to register (ABXY)

I first tried cleaning the membrane and pads on the board with isopropyl alcohol with no affect.

Then tried a replacement membrane which didn't work either.

I then examined the board under a microscope and found some of the legs on the socket connecting the bottom and top board have become detached from the board:

The legs actually have about a 1mm gap between them and the pads and only have a tiny amount of solder holding them on at the very tips making them quite weak joins. I counted a least 3 dodgy looking legs. I ended up adding more solder to all the legs on the socket (top and bottom board) to make a stronger connection (remember to use lots of flux to help stop bridging!).

It now works great again