Hello,
Three days ago I updated Avast Internet Security to the latest version and since then it blocks this site :
It is a football online manager game that I play for 10 years now.
I tried with Chrome and Firefox and the same problem. Immediately after I stop Avast, I can access the site.
Just tested it, the site works for me.
Yes, there are moments when it’s working, but after a few minutes gets blocked.
And after other minutes/hours I can access it again, but shortly it’s blocked again.
I believe it’s the firewall, I disable it for 10 minutes now and the site was unblocked immediately. How can I add an exception for this site ?
→ https://www.avast.com/faq.php?article=AVKB168#artTitle (Excluding files/websites)
Excluding the site from the general settings and the web shield doesn’t help, and in the Firewall settings I don’t find any exclusions 
→ https://www.avast.com/faq.php?article=AVKB25#artTitle (Firewall FAQ)
This has nothing to do with Avast Firewall.
I’m running Avast Internet Security and can visit the site without no problems (with Firewall enabled).
I suggest you run an Avast repair to ensure there is no corruption.