I checked this issue about 30 minutes ago and it is now working as expected .
I am suspecting that MalwareBytes installed on my system was the problem. Before I reported this problem to you, I had seen a message from MalwareBytes warning saying that a Page Builder page was dangerous. I told MalwareBytes to ignore this warning, Even though I did not see the warning again, I still had problems. Yesterday I rebooted for some other reason but did not recheck Page Builder to see if the issue persisted. When I checked today it was working correctly and I can save my work in Page Builder.
Note that I also applied new Helix and JCE Editor updates this morning before I checked so that also could have also fixed things.
Thanks for checking and responding.