Since v4.3.0 (Beta 2), or perhaps even earlier, I've experienced the following problem:
When I right-click the DisplayFusion icon in the taskbar (or the DF taskbar, itself) to bring up the DF menu, and then go to the Desktop Wallpaper Settings section, clicking on either "Load Next Image" or "Pause Current Images" in it brings up a window with the following message: "You must select the 'Load random images' option for at least one Monitor first." Selecting the latter to un-pause the wallpaper rotation still un-pauses it (despite still getting the message), but selecting it to pause the rotation doesn't pause it (it will stay un-paused). Selecting "Load Next Image" doesn't trigger anything, as well.
The DisplayFusion default hotkeys of "Load Next Random Wallpaper Image" and "Toggle Freeze Current Wallpaper Images" still work perfectly fine, though, doing what it's supposed to without getting the message window.

The problem was gone in the official 4.3 release. It works perfectly fine in the 5.0 beta, as well. I'm not sure if you found the problem yourself and fixed it or if the conflict was fixed indirectly somehow with the change of something else, but I'm glad that everything works again!