It is not required to reboot after changing a wall paper for it to take affect. If you haven’t already, Please update Samsung members app to latest version from galaxy store and send us an error report immediately after experiencing the issue from the Samsung member’s app -> Beta Feedback -> Error Reports to help us debug the issue. We apologize for the inconvenience and appreciate your contribution to the beta program.
Yes, after applying one theme, if you try and apply another it won't take. The only time it will take is the initial application of the wallpaper. So if you apply the photo as your background again and choose another color theme it will work. It just won't let you switch between them for the same background
