Thanks for the reply.
Avast just updated definitions to 200428-4 and subject popups stopped.
Also, the subject email (which should have showed up much earlier today) finally showed up on PoPPeeper, labeled ***VIRUS***(as usual), and we deleted (along with a couple others that arrived after the update); and PopPeeper is also working much better now.
Gladly the update seemed to fix things.
Also for a while (until restarted pc) after the fix and when opened Avast 'user interface' was getting notification that "Some shields are turned OFF. Please turn on your Anti-Exploit and Anti-Rootkit Shield for maximum protection."
Will wait and see on that one, or go to Protection/CoreShields later after determine if really needed and/or how to turn off if causes problems.
Take care.