Sharing a few points about using the layout editor/scene editor to create video with transitions between multiple scenes. Not sure if will bear on what you are doing, but anyway here they are, for what it's worth.
1. Before using the layout editor, make sure you un-hide all the tracks that will be used in the layout editor. If a track is muted(hidden) then the final output will just show a black square in its location.
2. Layout editor - to create a new layout, click New Layout, to add tracks to the layout, you can either go to the "Media Library" to add the tracks one by one,
or you can use "Auto Layout"->"Position All tracks" to add all tracks to the layout at once. A few other tips on using the layout editor:
Activate the Tiles Layout tab, you can select any video track and crop the video if necessary (this is handy to remove unnecessary/distracting backgrounds like a rotating ceiling fan)
To move/resize several tracks together in one group: hold Shift key and select multiple tracks, this will group the tracks into one group, then move/resize as necessary.
Remember to click "Say Layout" before creating another new layout.
3, Scene editor - this is where you assemble the various layouts created in the layout editor to form a video with multiple scenes.
When starting, there is only one scene (Scene 1) in the editor, chose the desired layout for scene 1. Then start playing the master video on the left, you will see the audio waves progressing at the bottom of the video.
When the video/audio plays, click on "Add Transition" at the point when you want to transition to the next scene. This will capture the timestamp of the transition point and fill it into the "Transition Timestamp" field,
and automatically add the placeholder for the second scene (Scene 2). You can adjust the "Transition Timestamp" field as necessary, and also adjust the transition style (I usually chose cross-fade at 0.5 or 1 second).
Now onto scene 2, chose the desired layout for scene 2, and then play the audio/video again and stop at the point you are ready to add the next scene. Repeat this process for as many times as needed.
When you are done, please MAKE SURE that you don't have an empty transition or scene at the end. That will mess up the rendering.
When all done, remember to "save Edits".
If for some reason you make a new edit on a track using tools under the "Edit Tracks" button (like rotation/mirroring, replacing with virtual backgrounds etc). Then all the layouts involving that particular track
must be re-done. Check through all your layouts in the layout editor, the track that's changed will now show up a gray box that says templates. You can add the track back from the Media Library.
That's about it, and once I got the hang of it, it works pretty smoothly now for me. I like how it works, and a lot easier than say iMovie, which of course have many other bells and whistles.