We got a professional to come look at this yesterday. I don't feel so bad at all the time I spent on this because it still took him several hours, so I wasn't crazy.
Ultimately we discovered that the insert in the Harting connector for RP1 was a little bit broken and when we thought the cable was well plugged in and locked, it was actually being pushed into the hood so the pins weren't actually making contact.
We couldn't tell anything until we took the connector apart and plugged the insert in by hand and the robot worked all of a sudden. That's how we isolated the issue to a bad connector. In hindsight, the connector could probably plug in both ways because it was just pushing into itself and it really can only go in one way.