I don't use plex, so I may be wrong, but I think you are supposed to assign different subfolders to different library types so it knows how to differentiate. You don't need different mappings for the container, just select the subfolders in the tree that you mapped.
Earlier you had /media, but now you referenced /data, so I have no clue how you have it set up.
I could be wrong though, I just know how Emby and jellyfin do it.