Version 2.1.1 has resolved this issue for me, as well. Thank you!

@tom, nope, now that you mention it all I copied over for my testing were PDFs, since that's about 97% of what I read these days. I spooled up my play instance for a few minutes and copied over an ePub and that worked fine. So, I am only experiencing this with PDF documents. Thanks for checking.

Forgot to mention, when I exit the book/document and return to it, I do not resume it at the previous location where I left off (presumably because the bookmark was lost).

Please let me know if there is additional information or troubleshooting steps I can perform to help isolate what about these circumstances is causing this issue. I don't see others with this issue, and this was a freshly-built VM for the purposes of testing this in a demo environment, so we can do whatever we need to do.