If you look at the white printing Q2 on the A side of that PC board, then look at the large blue resistor next to it, you can see a typical solder joint that hasn't flowed out all the way. You can see the brown flux built up in the middle of the joint around the lead of the resistor, and that kind of joint can cause intermittent issues that seem to resolve themselves as soon as you touch them.
Having said that, it's also really important not to resolder any of the LED solder joints, as that can damage the LEDs since they have been sitting around absorbing moisture over the last decade or so, and heating them up will boil that moisture right out and blow the LED.
