I thought I had made it clear in my last post. I did a full clean install eight days ago. Avast has run without issue since then. Today I got a restart prompt first thing after starting my computer. The last four or five times Avast has given me that restart prompt it has resulted in Avast being non-functional after the restart. So I am choosing to ignore the restart. After checking to make sure both the version and the definitions are up to date, and ensuring that Avast is showing the "You are protected" message when I mouse over the icon in the system tray, it seems like I will try simply ignoring the restart prompt. I am trying to save myself the time and trouble of doing a clean install. I can't keep my PC on forever, so I will shut it down at the end of the day as usual. If Avast is broken when I start my computer again after shutdown, then I will be forced to do another clean install. Probably that is what will happen.
As I wrote before: When I go to the update panel in Avast settings it says my application is up to date, with a release date of September 19, 2019, version 19.8.2393 - build 19.8.4793.544. That is the version that I downloaded from Avast on Saturday, Nov. 16, and installed that morning after the last failure. It seems like the problems started about a month after that release date, for unknown reasons. But I hope that the next version will remedy these annoying issues.