Just installed 19.8 on Windows 7 SP1, rebooted, then started Full Scan. Within a second it ended saying no problems found. Click to start a second time and running normal.
Another topic on this (for 19.7 I believe), if you run it again it is meant to run (as you have found) ok.
Looks like this little bug escaped the 19.8 update.
I think you should modify your first post and annotate it as being in avast 19.8 as I have don’t for this post.
Yeah, I had the same issues.