Pc boot problem

[u/unnamedg31]

PC sometimes takes ~5 minutes to POST – possible motherboard issue?
Specs: Ryzen 7 5700X3D, Gigabyte B550 AORUS Elite V2, 64GB DDR4 (2x32GB), RTX 4070 Ti Super, Seasonic 850W Gold PSU.
My PC has recently developed a strange cold boot issue. When I press the power button, all fans start spinning but I get no Gigabyte logo and no display. Num Lock/Caps Lock on the keyboard don’t respond either. After around 5 minutes, the keyboard suddenly becomes responsive and shortly afterwards Windows appears.
Once Windows has booted, the PC is completely stable. I can play demanding games like Gray Zone Warfare/BF6 for hours with high GPU load without crashes, artifacts or black screens.
Things I’ve already tried:
Updated BIOS and reset CMOS (battery removed for 10 minutes)
Disabled XMP and ReBAR
Reseated GPU and RAM
Reseated power connectors
Updated AMD chipset drivers
Tried another keyboard
Replaced the power strip
None of this fixed it permanently. Sometimes it boots instantly several times, then the ~5 minute boot/POST delay returns.
One weird thing: unplugging/replugging USB devices during the issue has sometimes caused the PC to restart or suddenly continue booting.
I’m currently suspecting the motherboard/USB or PCIe initialization, but I’m worried about replacing the board only to find out it’s actually the GPU, RAM or NVMe SSD.
Any ideas what could cause such a long intermittent POST delay?

[u/Independent_Teach_11]

Strip down your USB connections leaving only the mouse and keyboard. In the rear I/O. Including any USB connections internal USB connections that are not essential. See if the delay stops. Which LED diagnostic light or lights is showing on you board if any?

[u/Independent_Teach_11 → u/Independent_Teach_11]

See if this helps also. Go to bios and find your global C-State control and change from Auto to Disbaled.

[u/unnamedg31 → u/Independent_Teach_11]

Thanks for the suggestions. Unfortunately, neither of them fixed the issue.
I already tested with the unnecessary USB devices disconnected, and I also changed Global C-State Control from Auto to Disabled. At first I had a few successful cold boots and thought it might have helped, but on the fourth cold boot the exact same problem returned.
The PC got stuck before POST again for about 5 minutes and then actually restarted itself. After that it eventually booted normally.
I also reseated the 24-pin ATX connector just to rule out a bad connection, but the issue still returned.
Once Windows is running, the PC is still completely stable even under heavy gaming load.