With my little eye, an unrouted wire!
At the same time, only ONE unrouted wire. And it's even in a convenient location as I can just use a solder blob to fix it.
But of course that isn't the only issue. The 4 pin connector for the display was rotated 180 degrees and I didn't notice in time... Quick fix of course was to wire it up rather than using a pin header. I just hope none of the wires break off.
I assembled the PCB and attached everything to it last night. I even documented the process a bit with some pictures and video! Well, until my camera battery cut out around half way through the hard part. I'll work on editing those together later.
I tried to get the Trinket Pro working on my computer last night without any luck. It might be the USB cables, or just the computer. I will try with a different computer, but if that fails I'll be slapping my FTDI friend on the Trinket for now.