Hello,
thanks for reporting this issue. By default we only intercept HTTPS connections originating from browsers, so it is weird that this is happening.
-please check in GUI, Preferences, Shields, Settings in WebShield section, Scan secured connections from browsers only. Do you have the the option selected? Unselecting it breaks stuff; we will be getting rid of this option in the near future
-Have you tested that it is not enough to turn off web shield and you need to turn off all shields, or you are doing it "just in case"?
-Please could you send a support package (Help->Avast Technical Support -> Generate support package, note there that it is from you) after the issue happens?
-If you go to Messages' Preferences, Accounts, select your account with Apple ID, sign out, and log in to the account again, does it work correctly with Avast active?
We will try to reproduce this here, but if it fails, any information helps.
Kind regards,
Ondrej Kolacek