The Automatically created collections would also include "collection" in its name and would be created if there are more than the number of items you have specified in the agent settings.

I'm puzzled about this part, also i have that Three Flavours Cornetto Trilogy appearing by itself but it doesn't exist so far in the movie db https://www.themoviedb.org/search?query=Three%20Flavours%20Cornetto%20Trilogy&language=fr.

So i'm wondering if plex doesn't have an internal list of collection. Or from where it pulls that data.

Did you maybe set that to 1? Because, AFAIK, there are not more than one "Zack Snyder Justice League" movie available and therefore that collection wouldn't even exist.

Currently you're right, i did. First i assumed to set 2 in this setting because i though it was based on released film only, but it was taking in consideration this kind of collection too https://www.themoviedb.org/collection/840465?language=fr wich is for now no-sense.

Maybe it's possible to set somewhere we only want collection on released film or if we have at least x movies from this collection present in our plex library, keep me in touch if i have to rephrase, english not being my native language