This has been the most common question of the last 12 months.
Unfortunately, there's not usually an easy fix.
Could you send me the raw file? https://spaces.hightail.com/uplink/BellePhotography
This happens to everyone from time to time, and it doesn't necessarily coincide with an update either. Sometimes it just happens for no discernible reason at all.
It's a pain, I know, but you have to reload them from your hard drive.
Yes, what you're describing is the correct behaviour of duplicated screens.
The only thing I can think of is to manually force the issue using the little app I discuss in this article: https://www.damiensymonds.net/art_vista.html