Laptop's WiFi adapter refuses to communicate to 5GHz via channel 36-50

Question

I'm using an Intel 9560 Wifi adapter capable of a dual-band (2.4 and 5GHz) 802.11a/b/g/n/ac connection on my laptop. However, some three months ago, the 5GHz band randomly stopped working. I would not be able to connect to the gateway despite being ‘Connected’ to the WiFi (SSID shows up, but cannot ping gateway). Upon further experimentation, I found that my adapter refuses to connect to any Channel 36-50 connection with the 5GHz band. The connection works flawlessly on Channel 149. On Google Chrome, it manifests itself as the "DNS_probe_started" error and the "DNS_probe_no_internet" error. Every other WiFi-enabled device connects to the 5GHz connection just fine, so I'm pretty certain that the issue originates from the Intel 9560 card, or at least my PC. I highly suspect that the issue has something to do with Steam as well, i.e. the gaming platform (reasons below).

The most irritating fact about this ordeal is that I actually NEED the 5GHz band now. I've just finished the installation of two TP-Link Deco M9 Plus APs to extend the range of the free router given by my ISP, and connecting to it in my room is no issue... if you're using the 5GHz band, which runs on — you guessed it — Channel bloody 36. On the 2.4GHz band, I get an approximately 900% slower download speed.

It would be copacetic if any one of you could help me figure out what is wrong with my WiFi adapter. To be frank, being able to solve this without having to go through the annoying warranty process would make life a huge ton easier. The preponderance of information online has proved useless thus far... so here I am.

Stuff I've tried that temporarily fixed it:

1. Disabling the DNS service through regedit because I was unable to turn it off manually (options were grayed out for some reason). This worked for around 5 minutes before I was shown the error message on Chrome: 'ERR_NAME_NOT_RESOLVED'
2. Restarting the DNS service with the abovementioned method. This fixed it for around 30 minutes before the connection died again when I launched Steam.exe (i.e. the gaming platform).
3. Unplugging my external USB-connected hard-disk that I used to host a secondary Steam Library. After the aforementioned in point 1 happened, I decided to unplug the hard disk connected to my PC on the hunch that it may be something from the drives corrupting the Steam memory and somehow affecting the DNS. I restarted the WiFi adapter; lo and behold, the connection was steady. I tried to repeat this three times; Steam and the connection worked fine for the first and second time; both times, plugging in the hard disk and marking it as a Steam Library caused the WiFi connection to figuratively self-destruct... But on the third try, it didn't reoccur. The network stayed down even after removing the hard disk.

Stuff I've tried that has been totally useless:

1. netsh winsock reset catalog; ipconfig /flushdns; ipconfig /release; ipconfig /renew; netsh int ip set DNS: To 'help' sites asking people to even attempt the last command — why give it without arguments? Also, ipconfig /renew didn't manage to complete. It just stopped working on after three lines of code. It works perfectly when I'm connected to a usable WiFi connection.
2. Changing the DNS address: I've tried it; but in retrospect, why try something totally unrelated to 2.4/5GHz bands since the 2.4 band works perfectly?
3. Clearing browser cache: I'm pretty sure that this is not even remotely related.
4. Power cycling the router: useless.
5. Disabling the firewall: nothing.
6. Removing webfiltering software: I had installed Kurupira WF, but that was actually really recent; nevertheless, removing it fixed a glitched that disabled Insurgency from launching. Nothing related to the DNS issue though.
7. Changing proxy settings: zilch
8. SFC scannow: Nil.
9. Updating driver: Null. Even removed the whole shabang and reinstalled the driver. I've tried it using the original driver (from when it was working perfectly) as well.
10. Fully updating Windows: Zip.
11. Restarting: Yes. Nothing.
12. Changing the distance between my PC and the router: Yes. Nothing.
13. Checking if it's due to my 2.4/5Ghz bands being split into two connections: I've got two networks here, one 2.4/5GHz mixed and one split. Both 5GHz bands don't work. Setting the WiFi adapter to prefer 2.4 bands enabled a connection through the mixed WiFi network.
14. https://support.google.com/chromebook/thread/22790887: This one seemed quite similar to my situation. Unfortunately, no fix here.
15. Using the Windows troubleshooting tool: Frankly, this is one of the most useless, redundant, and superfluous tool that exists. Nope. It actually told me to turn on my VPN, hahaha. Which, of course, I tried, to no avail.
16. Changed WiFi adapter advanced settings.: Zilch.

That's all that I've tried, IIRC. Currently running Windows 10 1909 build 18363, driver version 21.90.3.2.

Succinctly put (TL;DR), my Intel 9560 WiFi adapter refuses to connect to 5GHz channel 36-50. And uhh... Pardon for the lackadaisical use of the language in this post; I haven't got too much time to be pedantic about it. I've spent almost a full 24 hours in total trying to solve this and my patience is wearing thin (with myself). I don't mind replacing my adapter too, and I'm open to any, if not every one of the suggestions you could provide.

(I originally posted a drastically shorter version of this on Reddit but I reckon that this would be the better place to ask this.)

Answer 1

Changing the 5GHz Channel Width in the Advanced configuration to 20MHz only solves the issue for good, probably by minimizing interference. Solved by @Ramhound. Solution cited from this Intel forum link.