This behavior usually means something is overriding the manual background choice (for example, a slideshow, Windows spotlight, or a theme sync/backup setting) and restoring the previous image.
To stop the wallpaper from reverting, configure the background explicitly and avoid dynamic modes:
- Open Settings → Personalization → Background.
- Under Personalize your background, select Picture (not Slideshow or Windows spotlight).
- Choose the desired image from Browse and apply it.
If multiple desktops are used, ensure the image is applied correctly:
- In Settings → Personalization → Background, under Recent images, right‑click the image preview.
- Select Set for all desktops (or pick the specific desktop that should use it).
Also ensure no slideshow or spotlight is active that could change the image again.
References: