Microsoft stopped supporting legacy Windows 7 on January 14, releasing a couple of updates and fixes in the end. One of them, as reddit users found out , removes custom wallpapers, replacing them with a black screen. Those wallpapers that are set by Group Policy for business users are also hit.
The problem happens after installing update KB4534310, removing which, you can return your favorite wallpaper in place. But then you have to leave the operating system without an actual (but last) important security update.
But, apparently, there is another option – do not “stretch” the picture in the wallpaper settings.
It is not yet known for sure whether the removal of wallpaper is a bug or features.