Just updated to 2806, and thanks devs b550-e cold start issue is gone now. On 2803 it is up to 3-4 reboots before post.
So silly of me, that I didn't look for a solution with G.Skill 4 ram sticks issue here in asus forum. I had this problem for about a year with F4-3600C16Q-64GTZNC and B550-E. I thought my 5800x can't run 4 sticks on 3600mhz. I did like "suizman" with his Crosshair VIII (set the voltage to 1.36 and disabling the "Power Down mode") and no more windows freeze, no more hard resets.
But 2806 didn't fix my mobo's USB 2.0 ports odd behavior. When FL680 keyboard is wired to usb 2.0, if you press (fn + ~) to factory reset settings (which is common action) kb will respond and work fine but you are no longer able to control your kb via FL's software (F. L Driver). Firstly I thought it's a kb or FLs software issue. Then I got PC75B+ and after I pressed (fn + esc) same sh*t happened 🙂 Akko Cloud didn't detect my kb. If you connect them to 3.0 ports there is software access, 2.0 still inaccessible even if you update bios or reinstall windows. I've tried it on another PC with a different mb and all 2.0 and 3.0 ports have access after factory reset.