Thanks for the screenshot - helpful. So it seems it's not even using Windows' Slideshow functionality – it manually changes the images, which I assume you have multiple images set in DF to rotate through. (Possibly possibly possibly, even when you've shut it down; could be some background service or Scheduled Task in play continuing the rotation; unclear.) In either case it does seem like a caching issue with Windows' PaintDesktop function, which when the wallpaper is changed in the manner in which DF is changing it, doesn't react fast enough and causes OUR caching to display some goofiness. In regular scenarios of changing the wallpaper via Windows settings or "Set as desktop wallpaper" context menu item, PaintDesktop's cache is already invalidated by the time the WM_SETTINGCHANGE message comes in, but with DF (or possibly any external app) changing it, there's a delay.
Odd because lots of our users use DisplayFusion, but we have not heard of this one before.
As discussed, I did take some additional swings at tuning the mechanism (we'll see if that helps/resolves – specifically, it breaking at random time intervals), in addition to adding just a ton of more debug code. So hopefully one of the two gets us closer or resolves. You can download it here:
https://cdn.stardock.us/support/uploads/Fences5_5.8.6.2-j149-Setup.exe
Per last time, you can turn on Advanced Debug Logging from troubleshooting and then install the new build, reboot, and it'll then be collecting data. After a sufficient # of times it has broken are collected, do the "Create Error Report Log" and send the latest and we can go eyes-on to look for clues for the next round of questions.
Ty for the help! Hopefully we can get this resolved or moved forward for you.