I'd suggest checking on the connection state of the small diode inbetween the SOT23 transistors to the left of the LED
Finally got around to poking at things - that was indeed it, saves some hunting


Was going for an angle view (
http://i.imgur.com/abKI0X4.png ) but I think the top-down one shows the problem pretty well; the pin wasn't wetted by the solder, probably for the reason you've pointed out before.. paste drying out.
Should be a simple fix with a touch of flux and a heat gun

That diode is one of the hardest parts for the machine to place correctly because it's such a friggin' small package, smaller even than the 0603. It's the littles thing on the board.
Indeed - That text at the top is the tiny "GekkoScience" silkscreen. The smallest I personally ever work with is 0402, which is plenty tiny and uncomfortable enough, and yet far from the smallest passives found in modern mobile devices.