@readee - I've uploaded a new test version of the plugin for you here
You need to use Preferences - Plugins - Load from file and select the zip file (don't unzip it), then restart and you should have the new version.
What this should do is use whatever date is in your book as the date that's displayed instead of trying to convert it. So some of your dates for books in Edit Collections may look odd and help you find the problem book.
Let me know how it goes.