Few things are worse than bugs that just don't make sense. I went over and over my schematic, I went over the CP2102N Errata, I went over my soldering and simply nothing was wrong. And after building up my second board (and most of a third) to get the same issue I was getting really frustrated.
One thing I hadn't tried was..... another computer. So the phantom USB issue I've been battling for weeks was actually an issue with my desktop. Fuuuuuuuuun.
The good news here is that I'm now not in a rush for a second revision. The only major changed planned was breaking out the few remaining pins. So as is, these will be acceptable for being deployed as relay nodes but until another revision is done additional sensors won't be possible. This is great!
The last remaining test I have is the battery charge circuit. Though I'm not sure if this will get used as I'm likely going to power these early nodes from an OrangePi Zero USB port that will be powered from LiFePO4 batteries charged by a #LiFePO4wered/Solar1 module.