So, I have two desktop monitors (one vertical) and a TV attached to my PC. My main use for DisplayFusion is to have two output profiles in Monitor Configuration. I've always only had one wallpaper spanning both desktop monitors, but recently wanted to have a unique image per monitor. I noticed that since the monitor profiles disable the desktop monitors when I change to my TV (expected and correct behavior), when I change back, Windows has forgotten my wallpaper for the 2nd monitor. I noticed that DisplayFusion has a wallpaper manager, and hoped it could fix this, or at least be a workaround.

At first it showed both the pictures when I had selected them through "load image", but unfortunately when I pressed Apply, they changed to solid black. And now no matter what I do, no matter the picture or even with URL loaded images, DisplayFusion just forces the Windows background setting to solid color. I can change the color in Windows personalization>background, but if I try to select "Picture" from the menu, DisplayFusion just changes it back to solid color. Making different wallpaper profiles didn't fix it.

"Autofix wallpaper images when wallpaper feature is enabled" on/off didn't fix like is suggested here. However for me if I disallow DF to manage wallpapers it goes back to normal.

Windows 10, DisplayFusion Pro 10.1.2 from Steam. IDK if relevant, but I have other customization software installed too: 7+ Taskbar tweaker, TaskbarX, and WinDynamicDesktop (latter is a wallpaper app so obviously I quit it before trying this)

OK so I think I kind of figured out what was happening. But some questions remain.

From what I understand in the linked article, it seems DF generates a combined new image from the ones you selected for each monitor, and sends that as one image to Windows in "span" -mode. And I suspect that it uses the original format (jpg, png, etc.) without further compression. And I had been testing it only with PNG images, which happened to be around and over 10MB per image. Those had worked with just the vanilla Windows management, because for that you select one picture at a time in fill mode, and right click on the one for 2nd monitor and click "Set for monitor 2". But it seems Windows has a size limit for PNG wallpapers. Selecting a single image at a time didn't hit that limit, but combining them into one in "span" mode with DF fills the limit fast. It seems the combined size limit for all the PNG images is somewhere between 14MB and 17.5MB. Not sure about that though.

So I just compressed them further, and it worked. Also changing to JPG works... on SOME picture pairs. For some reason, I got a pair of JPG's to work that have a combined size of 15.13MB, but another pair with a combined size of 8.11MB doesn't work, and still Windows resets to solid black. Changing the profile back to the one that worked doesn't fix it. I have to go to Windows personalization and pick an image instead of a solid color, and only then I can "apply" the DF profile.

Dunno, the whole thing acts weird. Some part of this might be a DF bug or Windows bug, some part just unfortunate incompatibilities.