This plugin is one of my "essentials", but maybe I have found an issue. I am on version 2.0.4 of the plugin, WIndows Joplin version 2.7.14.
When a note consists of a pdf, it shows nothing in edit mode, which is to be expected, and it shows a preview now in display mode, which is good.
However, if I select a different note that also consists of a pdf (or maybe that just includes a pdf), while in display mode, it locks Joplin up so I have to kill it via Task Manager.
If I switch to edit mode before selecting a different note, and then toggle back to display mode, it works fine.