First, you don’t say what your version number is, have you got the latest avast version, 17.8.2318 ?
https://forum.avast.com/index.php?topic=210678.0

Whilst there is something related to scans I don’t know if it directly addresses what you experienced, but during the last beta session it may have been addressed. It is certainly worth checking, but one thing for sure any fix wouldn’t be pushed retrospectively to old versions. Unless there was some sort of emergency update relating to it, but I can’t see that as I don’t know if that would fall under an emergency category.