I had the same issue a few minutes ago. The background objects might be in a different layer than the one that you’re working on in the default scene, and after looking at the video, that appears to be the case. Try having a look at the linked in scene and checking what layer the objects are on. When you return to the default scene, set the background scene to the linked in scene and make the layer that the objects are on visible. (For me, the layer that held the background assets was the fifth layer along the top row of the layer buttons)
If that doesn’t work, try enabling all of the layers until you find the one with the background in it.
You can also change the layer that the background assets are on by opening the library file and using the M key to move them to another layer (Wayne also mentions the Edit Linked Library addon in the Rivet Jump 1 video which makes that a little easier)
