I think you are mixing up what a “library” is.
In Plex you cannot have movies and tv shows within the same library.
A “library” in Plex is what appears at the left side of the web app.
There can be libraries of the types
movie
tv show
photo
music
Most Plex server platforms allow the creation of several libraries of each type.
Sorry if my terminology was wrong. My left hand side shows the libraries accordingly. So under Animations, all animations are saved there and all TV Shows are saved under TV Programmes. I am sure I got this right when I was reading the Plex forums.
@OttoKerner thank you for your time and assistance. I realised that my NAS may not be suitable to power the Plex. Whenever it scans, the NAS is not very responsive. And the continuous scan previously may have been a glitch somewhere. I might buy an android box to use the Plex, which is great by the way. Just sad that the NAS is not up to the task.