Ive been using and promoting/installing Avast for many many years now, and up until tonight I never had an issue with it.
I'm on windows Vista, and my upload speeds have been awful on this PC but somehow my wireless connection to my phone has normal upload speeds.
After TCP tweaks, advanced adapter setting changes and rebooting my modem, I finally found out by using a netstat -b activity.txt command that avast was using my connection. I decided to turn off avast and run the speedtests... and wouldn't you know, they are back to normal.
I updated to the latest version 2021, and re-ran the tests with no luck.
A bit of research shows "web shield" was an issue in version 2012 and supposedly fixed in 2013.
First image shows my speeds with avast running, and second without.... I'd love to continue using avast, but this may be a deal breaker.