I got more crash reports from other users, and eventually found that I could reproduce it on my devices. I think this is the problem:
I'm creating a new PDFLayoutView, and a new Document, then doing Document.Open() and PDFLayoutView.PDFOpen().
Then when I want to view a second document, I'm doing PDFLayoutView.PDFClose() and Document.Close(), but not recreating those objects. I'm just doing Document.Open() and PDFLayoutView.PDFOpen() with a new file.
If I change this to create a new Document object, that seems to fix the crash. I'm still able to use the same PDFLayoutView object.
I don't know if you'll consider this a bug, but it is a change from the older library version I was using before.