So my best guess as to the root cause: You pressed the bent-over LEDs down to the board *really well,* enough so that the little barbs just below the lens plastic cut through the solder mask, and into the traces below, causing some sort of short circuit. It may have damaged the IC, or the LEDs– not sure. I don’t see any other signs that point to a possible cause. Your soldering job was impeccable, and all of the components *seemed* okay otherwise.
And again, this is a new failure mode for us to see– we’ll obviously keep an eye out for things like this in the future.