I have a 2017 27" iMac that generally has one external display, connected to the DisplayPort port of a OWC Thunderbolt 3 Dock. This display is always connected to my mac.
Occasionally I will also connect a thunderbolt 3 external touch display for work. Up until today, that display was always considered display #3 and wouldn't affect the icon or window placement of either of my other two displays.
However, today I booted up my system with the external thunderbolt 3 display connected, and now macOS considers it to be display #2 as long as it's connected. All of my carefully arranged desktop icons that used to be on my DisplayPort external display now get kicked over to this thunderbolt 3 display. If I disconnect it, the DisplayPort display becomes display #2 again and the icons reset. It's very annoying!
I haven't found anything I can do to reset this behavior. How can I get my displays back to working the way they were before, with the thunderbolt 3 display always being display #3?