Excellent, I think the issue has been located. It's probably not the best idea to leave the double sockets in place, so I removed all four 40 pin sockets (since two had problems, I wouldn't trust the other two).
I have found in the past these can be tricky to desolder as they tend to hold into the tracks on the top of the board and can lift tracks or pads if you're not careful.
Time for a bit of a break before we move onto the next board. You can drink your weak lemon drink.....now.
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