Well, a casual glance at the tiny schematic icon of the project (used for now) and I think "Oh no! Did I cross the difference amplifier inputs? Sure enough I did. Below captures the schematic vs LTspice , and shows what is needed to fix this. Luckily these are all 0805 components so tombstoning a couple resistors and adding a couple bits of wire wrap wire (28g) is easy enough.

In other news, boards are done in fab at OSHPark and on their way, as is the parts order from Digikey. The laser cut acrylic box should be here today or tomorrow.