Windows 7 cold boot hdmi no signal

Hello! At first of all, sorry for my English.

I buy new fresh hardware. Asrock b450 Pro4(bios v3.50), Ryzen 5 2600, Sapphire rx580, G.Skill DDR4 16GB 2x8GB 3200MHz Aegis (F4-3200C16D-16GIS), psu Chieftec 850w, monitor Dell S2421HGF System is new and fresh.

I am understand that Win7 is old and Win10 is better. But i use Win7 and Win10 in dualboot. Win7 and Win10 fresh installed, it both fully updated.

So. Problem with Win7, cold boot and loosing signal. If i boot Win7 from cold boot, after Windows logo, video signal from hdmi is drop, on monitor i see text "no signal" Windows7 is still booting normally on black screen. I do reset and at second boot signal not drop. Signal drop only at first cold boot when pc is stay ~5-10min, and only at Win7, at Win10 signal never drop even boot it from cold start.

How i tried to fix signal drop:
-replace hdmi cable.
-using different radeon drivers
-upgrade and downgrade bios motherboard version

At last i found root of problem. I set my ram to XMP profile but not factory default 3200mhz, i set lower value 2933mhz.

I decide set XMP to default 3200mhz and voila, Win7 not drop signal at cold boot. Same happens when i use ram without XMP - signal not drop.

Signal is drop only when i use ram XMP and set not default 3200mhz, and 2933mhz.

I have question to guru, why is happens? What is the link between ram frequency and video signal?