First of all, the blue LED lead had solder just piled on top of it and to the side covering up the trace. I reflowed it and it is now working. No big deal, mistakes happen. But then I kept looking.
There were not one, not two, not even three rogue solder spots. There were a total of 8(!) rogue spots - some of them covering traces, some of them on the PCB with no leads even nearby and the overall soldering job was just awful. I managed to clean the PCB up and it is now nice and clean - but the fact that I even had to do so is simply ridiculous.

tl;dr If you are going to hand solder a board, make sure you don't get random spots of solder splashed everywhere.