How to find a problem if the sites of one server are unavailable?

Question

Computer networks

Good afternoon.
There is a server with our sites on it.
About a couple of months ago, I started having periods during the day when I try to open the site, but it returns an error with timeout. After an indefinite amount of time everything works. Then timeout again.
There are many computers in the office, we have one external ip, everything works well for everyone else, without failures.
On my Win 10 machine.
Firewall is disabled.
Antivirus - Windows Defender. I turned it off for a while when timeouts occur - it did not help.
In problem periods with a timeout, sites are pinged.
The problem appears when it is not clear.
How can you test a network or computer, or find software that is blocking or looping a request?
UPD1: The problem persists via wifi and cable