I'm out of ideas and I doubt it is related to the plugin we're discussing. Could you please paste a screenshot of the UI where you see all those authors with zero books?
IIRC books are counted by tags or series, but not by authors.
You can search books by name, authors or paths but that gives you still a list of books.
FWIW: the code that parses calibre json files is in
https://github.com/koreader/koreader...n/metadata.lua but I think it has nothing to do with your issue.