Why does the whiteboard window position display a background image?

There may be the following reasons:

1. No whiteboard in the room. In custom layout, horizontal layout, vertical layout, and floating layout, if the window does not specify a stream ID, the window is retained and displays a background image; if the window specifies a non-existent stream ID, the window is retained and displays a background image.
2. In custom layout, horizontal layout, vertical layout, and floating layout, if padding is set and the whiteboard exits the room, the specified StreamId becomes invalid, the whiteboard window will be retained, and the window displays a background image.
3. No whiteboard in the room, and recording whiteboard is set. The window displays a background image.