Huhm, that’s odd, yea maybe some issue with the router itself and since you have a spare that’s a good way to start. When mine croaked the sensor had come loose and was intermittently working as it slid in/out of the tube. It also rubbed a bit of the white paint off my commutator, so while I had it apart I repainted. I only know when it lost optical contact it took off at full speed trying to catch up with itself. You already know this, but check all connections and such that you made during initial install, things come loose.
A couple years ago I did an ECU update on one of my motorcycles (Yamaha R6). I had the ECU reflashed, added an aftermarket fuel control module, did a full exhaust mod, intake mods, ditched all the emissions junk, etc… It was a real beast! I was working with the guy who did the ECU flash to get my fuel maps all sorted out and all of the sudden one day, in heavy traffic of course, the bike just quit. Pushed it off to the side of the road, cycled the ignition, it started right up. This happened several more times, to the point that I didn’t want to ride it. The guy working with me on the ECU suggested I remove the O2 sensor and autotune module from my bike. I did so and never had another problem. Looking at the removed sensor and autotune module a few days later I noticed one wire wasn’t properly secured to the module(it’s like 6 wires into terminals and I didn’t tighten one). So basically I’d be blasting down the road, bike would vibrate a bit, and quit. I had sworn up and down that the install was good and there must be something else wrong with the map or ECU flash, I had to eat crow on that one. As has been said before, “Learning has occurred!”