Why does my computer stutters/lags on startup?

I recently (a few months ago) bought a new PC.

  • ASRock B650M-HDV/M.2 3.30 (type: UEFI)
  • Ryzen 7700
  • Kingston KF560C30BBEK2-32 2x16gb
  • Biostar RX 6700xt (bought this a year ago)

So, an year ago I got the mentioned GPU as an upgrade to my old PC. All was fine for the first few months, and then it wasn’t. All of the sudden the PC kept crashing and rebooting many times in a row(even before reaching POST!). This started happening while I was playing Skyrim(aka not a demanding game).
After trying many things, the only way to make that PC stable was to underclock the CPU and RAM.

When I ordered the new PC, I was hoping that my troubles would be over, but alas… From the first day this PC lagged and stuttered. BIOS was lagging, GRUB lags, both Windows and linux lags/stutters for a variable amount of time after startup. After 5-10 mins everything runs normally.

I don’t even know how to start debugging this issue. The window’s “Event Viewer” reports nothing, and linux does report some issues with AMD GPU driver, but this shouldn’t matter, since even the BIOS lags and there’s no drivers there.

PS. It is curious that I ordered this motherboard on 6.20.2025 (it was shipped on 6.23.2025 and I picked it up on 6.26.2025) and it came with the newest bios 3.30 that came out on 6.18.2025.

What are the odds of someone returning this motherboard as faulty, and that they just “fixed it” by updating its BIOS and sent it to me?