Encountered the exact same problem with my TUF Z390M motherboard, which evidently uses the same Bios, or is labeled the same at least. I too have a 9600k, and have had a very stable OC of 5.0GHZ @ 1.37v. After updating to 2804 Bios, OC settings were all over the place, and system regularly blue screened, even with optimized defaults set. I reverted back, v2804 is a mess. ASUS is way too vague on release notes.