It is easy for twitch to assign blame, but somewhat more difficult to actually pin it down.
What Avast program/s and version number are you using ?
Are you getting any error message or alert, etc. ?
If so if you can attach a screenshot or the error message to your next post.
Have you previously been able to use twitch with avast installed ?
If so when did this happen, etc.
Are you using a VPN ?