I've tried this on 4 different computers and have found the following:
1- If using Brave browser at swappa.com I am blocked from seeing the website while Avast is active
2- If using Chrome, Vivaldi or Firefox browser at swappa.com I can see and use the website with no problems
3- If I disable Avast I can see swappa.com using the Brave browser with no problems
4- All computer gave the same results
5- I've discussed this at the Brave browser forum and posted info there also.
This problem happens on some other sites also but only a few sites. Both problem sites I've seen this on do NOT use www.****.com but are simply https://****.com sites like
https://swappa.com so I don't know if that is related but noteworthy I think.