Why won't my PDFs open in Apple Books?

I save plenty of info as PDFs in Books. The last time I accessed one of these files was yesterday (7/31/24). Today, none of these PDFs will open. There is no error message. I’ve force restarted iPad. Closed the Books app. Same issue. iOS is up-to-date (7/30/24). I was able to access the PDFs after the update so the update doesn’t appear to be the issue . Called Apple—aside from restarting iPad and closing the Books their ideas—delete the app or reset network settings. Neither of these are good options for me.

[Re-Titled by Moderator]