As an engineer, I can't even count the number of times I've had these sorts of weird troubleshooting events. If you REALLY want to know, you'd swap the other base plate back in and see if everything still works. I understand perfectly that you're most unlikely to do that when you've finally got it working.
I'm sure there's an explanation, and I rather doubt there is a difference in the base plates. However, without doing that, nobody can say for sure what happened.
I know you're going to think it's a ID10T error, but I still get the dumb never-ending-spiny circle when I use the "wrong" wire box / backing plate.
I rigged up my 18' and 24' Gen 3 TWC wire boxes to their own branch circuits on their own 60A Square D breakers with #6 THHN throughout.
If I shove the 24' EVSE body onto the wire box from the 18' Gen 3 kit, it simply will not provision. But when I put it back on the right base, it works. And to make things worse... if I put the 18' EVSE body onto the 24' wire box, it provisioned fine as well. BTW, these Gen 3 units are both Tesla ones... not the more expensive J1772 variant.
When installed properly, I was able to master/slave these things where I capped the total 2 EVSEs at 64A. When I try to charge my Model 3 and Model X each at 48A, the EVSEs down-rate them each to 32A. Then, when one car charging stops, the other vehicle slowly goes back to 48A. So I'm almost smart enough to do this properly (almost).
As
@jjrandorin knows, I am the dumbest of the dumb-azzes in the Energy sub forum and I probably still am to blame for some variable that I can't explain. But for real, I have no clue why the "wrong" wire box will prevent provisioning. I agree the wire boxes look like dumb plastic/metal things that just happen to have lugs and a busbar.
Maybe the EVSE can't detect the 240v and ground with the wrong wire box? I have no clue. Anyway, proof I actually installed the things. Unfortunately I lack proof that I am not highly regarded.
PS... 64A is what my NEC load calc suggests is the maximum additional continuous load I could add.
PSS... Those are some damn sexy disconnects.
PSSS... Home Depot has sold out of 3/4" EMT. There's a
sriracha shortage and a 3/4" EMT shortage.