If you provide more details as asked for by Asyn (Reply #1), then we may be in a better position to help.
Also what type of scan were you running, Full Scan?
I will say that Avast and Windows update don't always get along. Although I had no trouble at all with my 1903 feature update, I did have an issue following the 1809 update. I had to uninstall then reinstall Avast then all was well after that.
You can initially try a Avast repair and see if that helps.
Edit:
I see j2roc has also posted here and from that see he is using Avast Premium.
https://forum.avast.com/index.php?topic=229187.0