Computer stutters and hangs for no apparent reason

[x64l]

Greetings all. I have a problem I've been having a hard time diagnosing with my Gentoo installation.
My hardware is a Thinkpad T590 (the i5-8365U model), and the Gentoo LiveDVD GUI works flawlessly on it, so it's a problem either with my system or kernel config (I build my own kernel).
I have only the internal 16gb of ram, nothing more, and a 256gb nvme. Memtest hasn't found any problem with the ram, and smarutils doesn't report anything being wrong with the nvme drive either.
It might be worth mentioning that my disk is fully LUKS encrypted with a detached boot partition, hosted on a USB drive.

From time to time my computer acts up; freezing, becoming extremely slow and laggy, sometimes hanging completely with the only exit being a forceful restart.
Most times what happens is the computer slows down to an absolute crawl such that typing into a terminal feels sluggish and commands as basic as ls print their results very slowly line by line,
like running Linux on an Arduino or something. When that happens, the computer remains slow until I either restart it or suspend and resume.
When I suspend and resume the lagginess is usually resolved, but the WiFi chip completely dies.
Sometimes I can reenable it using ifconfig, but most times it disappears completely, appearing neither in ifconfig -a nor in rfkill.
Sometimes I would get the lagginess, proceed to suspend and resume, and the computer would resume but immediately hang completely still, requiring me to do a hard reset.
The weirdest part - I'm not entirely sure what exactly triggers this. Here are the occasions where it had happened to me so far:
- Browsing the internet (note: I'm using Brave on Flatpak; usually happens while watching videos in the browser, surfing the YT homepage, scrolling on Reddit or 4chan, etc)
- Downloading a torrent file using aria2c (no gui at all, no other running tasks)
- Emerging or compiling a kernel (surprisingly the compilation speed stays the same, but if I do absolutely anything else the computer might hang (usually doesn't), but it does become sluggish and stay that way even after the compilation ends).

I've tried monitoring memory usage, cpu usage, temperatures, network usage, and io usage. The only two that seem to be at fault are CPU and IO usages.
As soon as either one of the CPU cores or the IO reaches 100% (or close) usage, said sluggishness ensues (however neither should be a reason for the computer to go on the fritz).
I've tried testing each of the above individually (and all together as well) using stress, but couldn't get the computer to freeze at all.
As I said, it happens when the CPU or IO reach 100% usage, since it also happened to me while downloading a torrent, it might be correlated to network usage as well.

In the last couple of days, merely opening up the browser and browsing some lightweight websites, then suspending and resuming (without there being any lagginess) has resulted in a hang various times as well.

I've been using Linux for 15 years at this point, ran it on all kinds of devices, and I've never ever had anything like that occur to me.

By the way, I've read somewhere about some flags you could pass to the kernel to help with the WiFi dying problem. All articles and forum posts boil it down to these two:
iwlmvm.power_scheme=1
cfg80211.cfg80211_disable_40mhz_24ghz=Y
It was hard for me to tell if these two did anything. It seems that before putting them, sometimes when I booted up the computer after a WiFi chip death the WiFi would still be dead, and with these flags passed to the kernel the WiFi seemed to be fixed with a reboot.
Well, I was actually trying to play around with these settings to study their effect, and the WiFi chip died on me, regardless of these kernel args, and no reboot fixed it. Left the computer off overnight and it now works again.

If anyone thinks the issue might have to do with X11, then for your information my setup includes a very basic xorg-server installation.
DWM as the window manager, ST as the terminal emulator, MPV for playing videos and Brave browser under Flatpak for web browsing. That's everything Xorg in my setup.

I've also read some mentions online of some people blaming lack of RAM for this. I don't quite think that's the case, I've monitored RAM usage closely and it never seems to even reach a quarter of the built-in RAM I have (16GB).
I also have a quite large swap partition of 50GB, and it's never even been used once. If you think the swap partition might be the cause, I've had the same issue before the creation of the swap file.

Another point regarding the culprit being the nvme or the computer's io or something is the fact that Gentoo's liveDVD worked perfectly with no problems at all.
However, when I decrypted my nvme disk to emerge -uDN @world and compile the kernel there wasn't any problem either, so it might be some kernel config and not the io.

I've tried Linux 6.11.4 first, then switched to 6.6.57, roughly the same version as the one on the Gentoo LiveDVD. Used the same kernel config on both of them (and obviously, the Gentoo LiveDVD used its own kernel.)

Please do enlighten me, any sort of help is greatly appreciated, as for the moment I can't even pinpoint what the actual problem might be. Thank you so much.

Here's my portage make.conf:

[Goverp]

The message at the end of your dmesg output lead me to
https://www.reddit.com/r/linuxquestions/comments/cnknq0/irq_16_nobody_cared_try_booting_with_the_irqpoll/
which might be helpful.
_________________
Greybeard

[pietinger]

x64l,

first of all: Welcome to Gentoo Forums!

Something is very strange in your kernel .config: You have this ->

[pietinger]

P.S.: I would suggest to use the newest kernel (6.11.6 at the moment) and go with this article:
https://wiki.gentoo.org/wiki/User:Pietinger/Experimental/Manual_Configuring_Current_Kernel
(after reading the first article // the only thing where you must deviate is the deactivation of the intitramfs support ... of course you need that.).
_________________
https://wiki.gentoo.org/wiki/User:Pietinger

[pietinger]

P.P.S.

Yes you also miss:

[x64l]

Thank you very much Goverp and Pietinger, highly appreciated! I'll try everything and report back tomorrow.