As per your concern, we suggest you kindly enable Auto update, if this setting is enabled the wallpaper in your current rotation will be updated automatically from time to time. And if you want the stories through the gallery app kindly select more images by the following steps: Settings > Wallpaper > Select Gallery > Choose more than 15 photos or videos to add to your wallpaper then select Done > Select Set on the Lock screen.
If the issue still persists kindly report the problems with a log file. To share a log file, click on the Samsung Members Application (Open Samsung Members Application > Support> Tap on error report > Type your query > Send).
