I was wrong about making the 503 errors disappear by deactivating UsersWP.
I turned on Divi Builder, tried editing the Location page (which I have set as the static home page), then tried exiting the visual editor and immediately got the 503 error.
I wasn’t able to navigate back to the admin section and kept getting the 503 errors.
When I finally manually (via the nav bar) navigated to the /wp-admin/ page, only then was I able to not receive the 503 error message.
Wish this would have led further down the “Ah ha, something with UsersWP is the cause of the 503 errors…” path, but, it didn’t.
Ugh…