Starting from today, whenever I try to submit my code, it shows “Sorry, you have been blocked”. I have tried these:

1. Use an incognito window;
2. Turn on/off proxy;
3. Use Firefox/Chromium;
4. Use a fresh Chromium installation;
5. Submit to another problem.

And while I cannot submit code, I am still able to access any other page (including posting this blog). Why this happens?

UPD: As a workaround, I switched to https://mirror.codeforces.com and it works.