No idea where that white residue comes from - definitely not from production. After wave-soldering, the pins of the connector are cut-down to "just longer than the board" with a specially-built tool so the pins don't conflict with the plastic case of the A500.
During QA, the card is inserted into two different machines, because there's so many different things to test. Should there be any trouble with the connector, it would have shown. Also, AmigaKit does another test - it's just their routine.
We've had a case with a journalist for a huge German magazine who was really unlucky with his A500s - both had trouble with the side-connector. For one of them, there was an obvious cut in a trace that goes to the side-connector.
With all the test-steps that the ACA500 goes through, it's very unlikely that it's faulty. If it is, you have your warranty. Please turn to AmigaKit to find out where the true cause of your problem is - this is not a support forum.