Internet cuts out on certain sites after the SECOND click, sometimes the 3rd.

Three different routers over ten years, wifi AND direct cable connections, all devices and all browsers. Right now there are:

MacPro laptop x 3, same problem over wifi with Chrome, Firefox, and Safari. None of these problems ever show up on our school wifi or any hotel wifi.

MacMini desktop, connected directly with a cable, I can see no difference between this setup and my MacPro, with all three browers AND Mac Mail, which uses Videotron's own email server. This last is why I'm suspecting Videotron is the problem.

Three iPhones and one Android phone, same intermittent wifi.

My son has a PC that he built himself, also with a direct Ethernet cable connection, and it drives him nuts that he is playing an online game and his connection just takes a one-minute break every ten minutes or so, causing him to lose his game. I don't know the details of his system, nor his gaming software.

If the problem has persisted over several routers, computers, and system upgrades, why do you suspect that the problem is NOT Videotron? Videotron is the only common thing in all this. My TV cable connection (also Videotron) is mostly pretty good. It's only the internet that is a problem.

BTW, thanks for all your attention here. I appreciate your effort to help me find a solution.