Funny, I've been dealing with a similar thing recently on my '20 SR/S, but with heated gear.
If I max out the heated grips, heated seat, gloves, and jacket liner, power to all of these cuts off until I restart the bike. No dash warning. It was right on the edge, as I didn't have the issue when slightly lowering the jacket power.
It has been getting worse over the past few cold days (lower power levels were tripping things), and it turns out my heated jacket has a short in it that I'm doing a warranty claim on. Hopefully the new jacket pulls less amps without the short and I can stay warm this winter!
Anyway.
There is a 10A fuse under the seat for the 12v Accessory circuit, so if more than 10A was pulled, I initially expected the fuse to blow, and to not get 12v Accessory power until a new fuse is put in. Since a bike restart resets power delivery, there's something else going on.
There is a comment in the unofficial zero manual that may explain things:
https://zeromanual.com/wiki/12V_Fuse_BlockGen3 models have a fuse block but the protection has redundant upstream components in the MBB, so the fuse block just helps with isolation.
It sounds like the FST platform has more than just fuses protecting the 12v wiring.
Either way, I think you're pulling more than the allowed 10A, and the bike is being nice and not forcing you to replace a fuse after doing so.
I've seen forum posts of people putting bigger fuses in for the Accessory circuit, but I'm not sure if that will work for us, since the MBB is monitoring things as well.
Other options I've seen include adding another DC-DC converter and adding another 12v battery.
