I'm using Calibre 3.35 on Debian Testing and I have all authors, tags, categories, series, everything automatically imported to my library for many books from many sources. Maybe there's a library dependency missing somewhere? Any debug logs?
I'm not at my main workstation at home, so I cannot compare now, but it's a very strange situation.
Perhaps you mean you use Calibre to download books from particular sources so Calibre exchanges metadata with the source server directly? I add files manually by dragging them to the Calibre window and expect it to extract metadata (like the book autor, title, ISBN and cover picture) from the file.
I usually buy ebooks through Humble Bundle, download all formats and then import them into calibre. For 2 of 3 formats the metadata will be extracted without problems.
Only one is usually lacking. I think it's mobi or epub, but never bother to pin it down because I just combine then in one entry anyway, and then the metadata will be merged together.
Calibre has usually no problem with extracting metadata from files, independant from the source.
I'm not at my main workstation at home, so I cannot compare now, but it's a very strange situation.