Don't mean sound like beginner as I not, but never had this trouble in few years, out bunch coon boarded, I got 2 with white big spots on flank. Scrape but tough layer on flank on just 2, the white spots are not fading, if take knife to them now, scratch mark all up. What best do ? Just let go like that, put a lil borax in it maybe ?they might eventually dry up

Yep, once in a while I'll have a gristle spot on a beaver like that. I just let it sweat out and wipe it down a little more often. Borax won't hurt. I like to let it go naturally as long as it's melting the fat out of the hide slow and steady. You won't have slippage as long as it doesn't cool and stay on the hide. Imo

I wouldn't worry about it, Dave. I've sold a lot of coon over the years that I noticed I'd missed some spots and the buyers didn't care.