Thanks guys; it ended up being a completely separate issue. I'll document what I did below in case someone has a similar problem in the future.
I thought maybe Hekate refusing to toggle AutoRCM could be related to the problem, and I guessed...
I wanted to be able to boot from a powered-off state without a computer or jig.
According to Hekate, AutoRCM is off. I can't even enable AutoRCM via Hekate - attempting to toggle just says that it is still off.
Yep, it's a picofly - picofly...
Hi, I installed a Picofly in an unpatched Erista Switch, and it works fine if I power the Switch on while it isn't plugged into anything. However, if it's connected to a charger, the Switch boots into RCM mode and stays there. There are no lights...