I’ve played around a bit with a multi-board setup (v2,2 & v2.3 CM boards) as I’m running multiple CAM standards (GRBL & ESTL). Since I’m using a “more prone to dropout” v2.2 CM board, I wanted to identify and mitigate the sources for USB dropouts.
In my experimentation with wire proximity, I can guarantee a dropout of comms if the Dewalt power cord is anywhere near any DC wiring (servo or limit switches) or gantry framing. Physically isolating DC and AC wiring will help mitigate the back EMF noise, as will grounding the machine and powering your router from another AC branch.
I have also run ferrite cores on all the wiring. With these steps I’m running this older v2.2 with extreme reliability.
YMMV