Ew. I was thinking of getting an SGX+Everdrive, but now I'm not so sure. What the hell is the TED doing to the ROM data before it hands it to the hardware?
Given the shortage and cost of decent 5-volt memory, the TED v2 is using modern 3.3V memory and components, and then using a 3.3V-5V buffered level-shifter to talk to the HuCard slot.
There's nothing wrong in-principle with that, but it has proved to be much more sensitive to the actual voltage on the HuCard slot than older designs.
Basically ... the v2.4-and-higher Everdrives seem to be pretty solid, but none of them play well with crappy Multi-Region mods that degrade the standard voltages or slow down the bus signals too much.
I've not had any problems with the TED v2.3 on my unmodified SuperGrafx.
The TED v2 specifically states on the site that it's not guaranteed to work with consoles that have 3rd-party region mods.
Basically, neither the TED, nor a region-mod are original spec equipment.
For now, it seems like you have to pick one or the other. Trying both sometimes works, and sometimes doesn't.