Help needed: Preview Bug?

Hi all,

I recently started my courses again and these involve a lot of PDFs. I have noticed a problem that has sometimes happened in the past, but I have not had anything like the extent of this issue in prior semesters.

I usually look at PDFs in Preview, but now when I load a document it often says "Document empty group". So you can't tell whether something is text or an image; it just isn't there, even after reloading.

Has anyone else noticed this recently, and/or is there a workaround?

Thanks,
Daniel