Why are some sites not logging in?

Question

Computer networks

Some strange glitch recently, when I go to some sites to log in, I go to the site itself, but when I try to log in, it gives an error. At the same time, if I reconnect to another Internet, then everything becomes ok. I think if the ISP blocked some sites, they would not open easily. And here the error is at login and at other pop-up forms. Tried clearing browser history. I also tried using 3 different browsers. Everywhere the same problem.

Answer 1

try to go to them through vpn - if it works (especially since it works from another Internet) - apparently the provider is blocking something
Authentication does not have to be on the same domain as the site