As in, you dragged 10K PDFs to Zotero? If it got stuck, just restart Zotero, select the unrecognized items, right-click, and choose Retrieve Metadata for PDFs.
If it gets stuck on a specific PDF repeatedly, we'd want to see a Debug ID for that after restarting Zotero.
If it gets stuck on a specific PDF repeatedly, we'd want to see a Debug ID for that after restarting Zotero.