Unable to boot scan keep showing error screen not loading.
Additional sc
Additional sc
Not sure why you would need to do a Boot Time scan.
There are several topics relating to this problem and could be related to your issue.
But Your system may not be able to do a Boot Time scan with the new means of running it in the Windows runtime environment. See this topic - https://forum.avast.com/index.php?topic=321784.0 and my reply #1 in the topic and subsequent replies in that topic.
Also check out this topic - https://forum.avast.com/index.php?topic=320488.0