It's working again!

1. As the Windows update had been run 24 June, I restored a backup from 23
June. Alas, problem continued.

2. I then restored a backup from 21 June. Alas, problem continued.

3. I know that I did a COPY/PASTE as recently as 19/20 June, so I then
restored a backup from 16 June. Problem fixed!!!!!

I then updated KIS, problem still fixed!!!!!!
I then ran Windows update, problem still fixed!!!!!!!

Evidence is that something broke between the 16 and 21 June bckups, most
likely on 20/21 June AFTER I did a COPY/PASTE on 19/20 June.

I am now backing up the system.

I guess that there could have been a virus that KIS did not detect.
Any other suggestions for cause of the problem?

When the backup is finished, I'll turn on Automatic updates in KIS.