Windows 10: Set Desktop Background "Span" fit setting not functioning.

I would like to set a single image as my desktop background across my two monitors. For this purpose I have prepared a single image sized to fit the screens exactly - it has a resolution of 3840x1080 pixels, i.e. two 1920x1080 screens side by side. When I select the image in the "Personalisation - Background" screen, and set the sit to "Span" as seems to be the official instructions for this process, only the left hand end of the image is shown on both monitors, almost but weirdly not exactly the same as when I select the Tile fit option. I have considered working around this issue by splitt

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Slideshow wallpaper displaying as span when set to fit

I have my wallpaper setting running as a slideshow on Windows 10 set to Fit. I'm fine with displaying different images on each monitor, but after a little while it will start displaying only one centered between the monitors as though it's set to Span.
As soon as I open the Settings app to fix it, the background resets itself and goes back to working correctly. Any solutions would be helpful.

 

Background Settings

I set my background with "Slideshow" from a folder of pictures and I set the fit to "Span" because I have 2 monitors. Windows changes it at least twice a day. Why?

 

Desktop background settings won't save

Hi. Am having the issue where the screen is stretched. I right click on desktop and select personalize. It brings up the setting page and is defaulted to background setting. I see the preview of my desktop with a backrgound drop down box set to picture.
There is a choose your picture option and then choose a fit. The choose your fit drop down box is set to stretch. If i change the background option to either the colour or slideshow option and close the settings window....it accepts those changes, but remains
stretched. If i repeat those steps and change stretch to centre or tile or fit and close the window, it does not accept the change and when I go back to the persoanlize background page the choose a fit drop down has returned to stretch. Wtf?!?! What do
i do. This just happened. "All by itself". I have restart and i can tell you it is the same experience from either of the account profiles set up. Please help. Thanks.