Internet (both Ethernet and Wi-Fi) having troubles ONLY for Win10

I'm sorry for the amount of text below, but I just want to describe this quite unique problem. It might look like a common thing, but it's really not.

Problem itself:

Sometimes, when trying to reach any resource on the Internet, I'm receiving a timeout error. It repeats for 10 seconds, then everything is fine.

If I'm going through SpeedTest it says either that socket error occurred, or sets download or upload speed (depending on which one is being tested) at 0 Mbps.

However, existing connections work fine. I can talk in Discord without any problems, as well as play some online-FPS games.

In such conditions, both Win's and router's resource managers show the speed of <2MBps.

Happens with every browser (including IExplorer) and every app.

Hardware part (or why it's an OS problem and not HW\ISP) problem:

I have 2 machines running Win10 Enterprise 1803. The second one was made of cloning the first one, since I reinstalled SSD not so long ago.

Both of them have the same issues for both Wi-Fi adapter or LAN-ports.

The Parent-machine also has a dual-boot with Win8.1 on it and it works perfectly fine, even better than 10.

Obviously, this machine has the same specs as the one with win10.

Also, when I connect with my Phone to Wi-Fi, not it only shows better connection stability than the Ether-connected Win10 machine, but it also shows better connection speed at high distances (e.g. from South-Ural to North America). This exact machine under control of Win8.1, however, shows speeds even faster.

The same problem with bad stability and speeds happens, when you connect Internet cable directly to PC.

I've talked about it with ISP support and with two of their engineers, and they don't know what causes it, nor how to fix it.

I've been using this OS for a 2 years or so and had speed problems all the time, but the stability problems occurred only a month or two ago.

Previous Win10 state:

1. I never had any antivirus on this system. Usually, once in a year or so I install Kaspersky's pack, which used to deep-scan system and removal right after.

It doesn't leave any trace after.

1.1) I use process explorer's hash-sumbit to virus total instead. At this moment it shows no problem, except MSI afterburner and ASUS aura.

2. I had the firewall first disabled, then disabled by group politics and then removed by third-party software along with win. defender. As the result, I never had my connection blocked by it.
3. Never used a proxy or VPN.

What I've done so far:

1. Checked for adapter problems using windows tools. There were no problems.
2. Disabled IPv6. No result.
3. Disabled file-sharing, remote access, and PC'S detection from the network. No result.
4. Re-checked for driver update. It said I have last version of it. Manually updated driver caused no result as well.
5. Uninstalled NpCAP, WireShark, and Oracle VB. No result.
6. Disabled Energy Efficient Ethernet in Adapter settings. No result.
7. Disabled every WOL too, just in case.
8. Made some diagnostics by Intel's adapter settings. It said that everything is fine.
9. Disabled Larg-Send-Offload v2 for IPv4. No result.
10. Changed Reserved by system bandwidth in GPEDIT, allowing system to use 99%, 50%, 1% of bandwidth. No result at all.
11. Tried to Update my Windows. Causes some kind of error at 99% which results the revert of it.
12. Updated BIOS. No result.
13. Added logging for Filtering Platform Packet Drop-in Audit. When the problem happens, there is nothing about it in the event log.
14. Flushed DNS, made a winsock reset and resetted TCP connection settings.
15. Cleaned hosts file. No result.
16. Tried running in safe mode with Internet support. Problem still ocurres.
17. Tried making a new user as well as using the hidden administrator account. No changes.
18. Compared Win8 and Win10 settings of TCP interface using "netsh interface TCP show" command. There are few different options.

18.1) Set netsh interface TCP set global autotuninglevel=disabled and back to default. No result in any case

18.2) Win8.1 doesn't show anything under "show supplemental" as well as it has some kind of parameter setted to "none"

Win 10 supplemental setting: https://imgur.com/a/9Z6tGdm

It says "Поставщик дополнительного компонента контроля перегрузки". I can translate it as "Provider of addition component of controling the overload", but not sure how exactly its called in English.

19. Changed IPv4's DNS to Google's DNS. No changes. Changed it to auto-receiving. No changes.
20. Re-checked for potential viruses. No viruses.
21. Disabled every single third-party process, that could interfere with the connection. No result

Is there a chance that the problem may be caused by the corruption of certificate storage?

I'm studying as SysAdmin right now and understanding of this problem and its solution may be required in the future.