PC extreme lag, slow image build-up during/after (re)boot

Today’s update: swapped the GPU with my old one (the R7 260X). This all the usual driver wipe in safe mode, installed legacy driver, rebooted a couple of times (the necessary ones from booting into safe mode, reboot from DDU, reboot to leave safe mode, reboot during the driver installation) and then 2-3 user-initiated reboots and a cold start. Worked fine. No staying at a certain q code for longer than required. Felt alike normal post/boot times.

Then I put my RX 480 back in and did the same thing (just with current driver, not legacy). Same result. So far it works fine, even after couple reboots. The only thing I noticed is that the VRAM frequency got stuck at 300MHz again. Happened before. This time a reboot fixed it. Also seems to happen to others too without the GPU being faulty, just Radeon shenanigans. But who knows, maybe in my case it’s caused by the GPU?

Anyway, since then my PC - as many times before WHEN it posted/booted normal, ya know, like after 1-3 reboots where the lag/sluggish image build-up would occur - worked fine.

One thing that was new before I swapped the 260X in was that I checked the PSU cables if any are loose (one was a tag bit but that was maybe 0.25mm, not even enough to disengage the locking mechanism). After that the q code showed “8”. Just eight. Not “08”, just “8”. Couldn’t really find anything specific about it. Some say CPU, some say BIOS, someone had a m.2/Windows installation causing it bc it worked fine again after replacing the m.2 and putting a fresh Windows installation on it (so they can’t say for sure which of the two caused it).
No idea what it is/was in my case cause when I hit the reset button it posted/booted into Windows.

In mobo news: decided to go with a X570S instead of one with a chipset fan. My room is way too dusty, no matter how much I clean it (a big portion comes in through the window even through the window screen). So having a tiny ass laptop fan on the mobo under a perforated cover would definitely be a pain in the ass to clean all the time. Or even cause issues. Plus, on the L1T forum are 2 people who mentioned to me they had theirs fail on the C8H.
Ordered the C8 Dark Hero only to have it get stuck in order limbo. When I ordered it there was no indication that stock was low. Now it says “1 left in stock” but you can’t even order it from Amazon as the seller anymore. Order confirmation email and the order entry in my Amazon account both say “we’ll let you know via email once we know when we can ship it”, so…no new mobo for now.
If after some more testing it turns out that my mobo needs to be replaced because it’s faulty (and not because the warranty period is over and it might be faulty) then I’ll either get a B550 with the features I want or one of the MSI X570S.

tl;dr - swapped GPUs. works fine for now. dunno if it just needed to be reseated. still don’t know where that electric crackling noise came from (the one when my PC shut down afterwards 2 weeks ago) or what caused it.