Thanks for the reply. I tried adjusting the Power and Battery settings (including setting to Never), but it did not fix the problem.
However, I have now resolved the problem by setting the screen saver settings. See the following link for instructions.
The wait time was set to 1 minute. I reiterate that I did not do this. I had not changed anything. I have seen several posts on this forum where people have indicated various changes have occurred after Windows updates, but I cannot confirm if this is when my problem started. Sometime had probably elapsed between the last update and when I was doing work that required me to stop work on the computer for more than 1 minute (but I can't confirm this either).
I only changed the "Wait" time from 1 minute to 10 minutes. I left Screen saver option as (None) and On Resume box checked as they were when I opened the dialog. See the screen shot below.
I will try to edit the original post here to show resolved.