Why is coursera.org not loading?

Question

Computer networks

Hello!
I'm trying to study at https://www.coursera.org/ , but the joy of learning is overshadowed by the fact that the courser regularly slows down wildly, and sometimes refuses to load at all. And everything is fine with the mobile Internet, that is, the problem, as far as I understand, is in the provider (or in my router?). But since I am an oak in this topic, I have absolutely no idea how to find out the cause of this phenomenon, much less how to overcome it. Here I would like to know the answers to the above questions.
Chrome writes Timed out waiting for a response from the site www.coursera.org. And wget writes Unable to establish an SSL connection. Also https://www.strava.com/and some other sites load poorly (but not so catastrophically), but most sites (including https) work fine.
Thanks in advance.