This is not a WebFlow issue… and it will probably not affect most people.
It’s for those who use Quick Cast to capture screens for video.
I have a couple dev systems… on this specific system - I changed my monitors from
qty(1) 24" Asus HDMI + qty(1) 24" HP HDMI
to
qty(3) 24" Asus HDMI.
Previously… with QuickCast… I could select from a list… which monitor I wanted to capture.
Either the HP (left) or the Asus (right).
My monitors are all the same now (all Asus 24")… and the list only contains 1 monitor (Asus)
And I can only capture from the far left one.
I cannot capture from the other 2 monitors 
I removed the 2 new Asus Monitors… and reconnected the HP… and the problem went away.
Just FYI for those using Quick Cast.
It seems to be a bug in Quick Cast.