I have 3 sets of wallpapers for 3 monitors (9 in total, 3 per monitor). The wallpapers in each set should always be shown together. This effect can be achived by enabling "Enable desktop wallpaper slideshow" on each monitor and also enabling "Show in alphabetical order" to get a deterministic rotation of the wallpapers.
To clarify: Lets assume Wallpaper sets A, B, C and monitors 1, 2, 3. (A1, A2, A3), (B1, B2, B3), (C1, C2, C3) should always be shown together. This works with the settings described above until one monitor gets disconnected or wakes up a little to late after sleep. In such a case I will i.e. get the situation (A1, B2, A3), (B1, C2, B3), (C1, A2, C3).
I then have to play a game of disabling the slideshow of monitor 2 and clicking "Apply" until the wallpapers are synced again, after which I can re-enable the slideshow and leave the settings.
Since this happens quite often, it would be great if there was a way to hard code that (A1, A2, A3), (B1, B2, B3), (C1, C2, C3) should always be shown together