Download the latest update here:
https://forum.avast.com/index.php?topic=201729.0

Offline installers:

http://files.avast.com/iavs9x/avast_free_antivirus_setup_offline.exe

http://files.avast.com/iavs9x/avast_pro_antivirus_setup_offline.exe

http://files.avast.com/iavs9x/avast_internet_security_setup_offline.exe

http://files.avast.com/iavs9x/avast_premier_antivirus_setup_offline.exe

I don’t strongly recommend downloading the online installers they are glitchy and buggy, check first if the digital signatures is properly signed if the signature is invalid don’t install

EDIT AND UPDATE:

Download Avast Uninstall utility and do a clean uninstall and reinstall it again using the custom mode.

Attach the logs found on Program Data/Avast Software to clarify and we see the problems with clarity. Thanks