see the screenshot here Imgur
When attempting to set individual wallpapers per monitor, all selections show the same monitor.
i've previously installed displayfusion, Actual Multiple Monitors, and I am using a displaylink usb adapter for my 3rd monitor. I do not know when this last worked. I may need to reinstall displayfusion. actual multiple monitors has been uninstalled along with displayfusion. i have also reinstalled my displaylink drivers and rebooted multiple times.
I feel like displayfusion caused this issue. i also use LogMeIn, teamviewer, and screenconnect. the issue started months before we started using screenconnect.