Error 521 & Your connection isn't private

[Music Addict]

I notice that these errors occur at my first 2-3 downloads on IMSLP from the point I start Microsoft Edge, even with the latest version.
However, Mozilla Firefox doesn't seem to have this problem.

Here're some screenshots I took:

28 July 2020 at 10:32 a.m. (Kuala Lumpur time zone) - Three attempts to access the PDF scores by clicking on the same file link:
1st attempt - Error 521 Web server is down
2nd attempt - Error 521 Web server is down
3rd attempt - Success

30 July 2020 at 10:59 a.m. (Kuala Lumpur time zone) - Another form of the problem
Your connection isn't private