How to increase the stability of your Internet connection?

Question

Computer networks

Connected to ISP via cable. Announced channel 100/100 Mb/s.
In the apartment, the Internet is connected through a DIR-825AC router.
Further, a wired connection to a PC, and wifi to all mobile devices + sometimes a laptop.
Next, we will talk about the situation when the PC is turned on and the Phone is in a passive state at home (it does not download anything).
At this speed, the Internet should work normally on the PC + the game (World of Warcraft, Tanks, etc.) should work + watch 720p video (second screen)
OR 720p video from YouTube + game.
The problem is that even just a video in 720 quality is often interrupted if I, for example, clean my mailbox. This is very sad, not to mention the quality of 1080p.
Sometimes it happens that the channel stabilizes and I can do it all at the same time (both the game and 1080p video and the browser is open on other tabs like VK, etc...)
How to fix these temporary dips? what can be the problem?
Background programs are only local, of which only Kaspersky can really affect. But it works all the time, but the Internet either works fine or it doesn’t work (it was terribly slow and connections are interrupted).
As an additional factor, there is the DISCORD program, when the connection is interrupted, even the discord is disconnected from the voice chat.
Also, I tried to analyze the traffic myself, installed programs that display the traffic used by programs and the current speed by programs. According to the program, the traffic on the computer is not used at all (the channel is most often clogged by no more than 25% even when watching a video, at a time when the connection is stable)
IMPORTANT: I ​​tried to disable Kaspersky and all all all programs. And, as a result, either the Internet worked stably, or it works like shit as it worked.
I'm completely exhausted
Help, maybe someone knows where to dig at least ???

Answer 1

The processor is not enough for all tasks.