PC power cycles once before starting from cold boot.

[MightyMase04]

Hey! I've been dealing with this issue off and on for a while now. I'll explain the problem, the frequency, and my own suspects.

specs:
r7 3700x,
gigabyte b450m ds3h v2 motherboard,
Gigabyte Eagle RTX 3070ti,
4x8 OLOy DDR4@3200,
Team 1tb nvme TM8FP4001T (boot drive),
2tb sata SanDisk SSD Plus (secondary drive),

Seasonic Focus GX 750 psu,

the problem: whenever I start the PC from a safe, proper shut down, the PC powers on (all fans and LEDS come on and the monitor is woken), it all cuts back off, then about a second later the PC starts normally without myself doing anything extra. It also does this upon a restart into UEFI/BIOS from windows, but not during standard restarts, or from an improper shutdown, like via crash or sudden power loss.

The PC starts normally after reaching post in the video.

 

the frequency: long periods of every single time, but also long periods of normal behavior. I actually thought this had been fixed by an update or something a few months ago because I noticed that the problem just wasn't happening anymore. BUT as of a few days ago, nothing changed AFAIK, the problem has returned, bothersome as ever.

the suspects:

• weird RAM
  • I'm running a memory setup of 4x8 sticks of ddr4@3200mhz. These were two 2x8 kits bought separately months apart. They are matching sets, but there could be a difference between them causing problems. I had experienced some issues with this memory in the past with the default XMP profile, but swapping around the sticks I had in the 1st/3rd and 2nd/4th config fixed that issue, confirmed by multiple very long memtest64 sessions.
    
    I'm thinking that the reason that it stopped happening for a while may have been because I removed all but 1 stick troubleshooting something else a while back, but I'm not sure. The problem is back, though, and I have already tried switching sticks around, which didn't help. Come to think of it, I have not tried with just one stick of memory yet. I will try after this post and report back.
• faulty PSU
  • my 750w PSU is a second hand unit from a trusted owner who had no issues out of it, was just ready for an upgrade. but even a brand new PSU can have issues so i'm not ruling it out
• weird BIOS update??
  • I remember thinking, but never managing to prove, that this all started after the BIOS update I upgraded to get ReBar support when I upgraded my GPU a while back. I've tried updating to newer BIOS, never did anything. I also tried going back to the oldest BIOS that supported ReBar, but that didn't fix it so I upgraded to the then-newest update. I am currently one revision behind, bios v F64 vs F66.
     

Anyone experienced anything like this before? It's not the end of the world but it's generally frustrating and I can't help but feel like it causing additional wear on my PC.