3D FlipBook - Can't upload or edit PDFs in Details section

Hi! I'm not sure if installing a new File Manager plugin recently might have caused this, but I can't upload or edit PDFs in the Details section now. I'm unable to even click or expand the Details in new and old books. I tried installing another flipbook plugin and noticed that I can't upload PDFs either. My Media Library also doesn't display any of my files.

I've deactivated and deleted the File Manager plugin, but still can't resolve these issues. Has anyone experienced anything similar or have any advice? Thanks!