This thought just occurred to me as I glanced over a notification that came in on another thread ("...there does not seem to be a way of seeing exactly which layout is in action for a page, even by inspecting the code." Source)
What about a new little icon in the admin menu that either links to a separate page or has a little dropdown info pane with details about the current page you are viewing?

For example, all in one place, info (and potentially links to edit/adjust) about the:
- Layout used on this page
- Theme
- Content type
- etc.
That may be overkill but thought I'd throw it out there to see what people thought.
Recent comments
@yorkshirepudding, In the end I fixed it by deleting the config/active folder contents, copying the config/staging/ files into config/active, importing the database again and clearing the caches...
Importing the staged config throws an error: another field with the same name already exists
Thanks, I have to go out now, I will try later on and report back
Importing the staged config throws an error: another field with the same name already exists
Hi Francis. Yes, what config do you have in staging for it? You might have configs like: field.field.field_video_embed field.instance.node.page....
Importing the staged config throws an error: another field with the same name already exists