Hmm, I really don't know. So Corona does shoot to 250W, but that itself doesn't crash it if I understand, it's only after certain while (10 +/- minutes) when it does ? That would rule out power limits and point more towards cooling.
I can feel the frustration, when I've setup our 2990WX which we really needed at the time and it didn't even work with the public bios I was close to insanity. Every wasted day counted, 5k euro spent and shit is not working. If the private beta bios didn't solve my issues I was prepared to start with parts swap (first motherboard).
Hope this will be solved for you. One more try, maybe contact them through website ticket as well, there might be beta bios likewise.