The bib versus the Zotero file: 3488 vs 3816 entries, after cleaning up not more than 50 duplicates in the bib and deleting maybe 50 more irrelevant entries.
On your last point: yes, the few new PDF files that I imported had very, very little metadata come through. Even on recent (2018 onwards) publications.
I hope that is fixed soon. Otherwise I’m very pleased with JabRef