Sorry about your problem, I can't add much especially since I don't ken your nutrient program, but I would add that at this stage in flower, I'd get the RH below 50% to avoid any mold issues with your buds. Last time I got bud rot my RH got out of control due to getting sloppy while flushing, spiked up to 65% for a day, and that was all it needed, although I was also growing a super-dense bud strain, Immense Bulk, so that didn't help.
But good luck man, hope it doesn't get much worse, or that you can get across the finish line before it does.