The problem with the first PCB was that the ground pin on one of the force cell amps wasn't connected!  It was on an island of copper, and thereby didn't connect up with the ground plane.  I re-oriented the force cell amps and everything is working now! 

Next step is to integrate 3.3V solenoid control for dispensing liquids, using a circuit we've previously built:

https://hackaday.io/project/156847-simple-pcb-to-control-a-33v-solenoid

And then spin a nice purple board!