The plugin takes a long time to load the first time it's called in each editor session.
I have already tried breaking the HTML generation off in to a promise so that I could add a loading image to improve UX, but the promise resolved almost instantly suggesting the issue is with the way tinymce renders the window on init.
The tinymce docs are notoriously lacking, so I'm not sure where to next with this. If any experienced tinymce plugin developers see this and have any suggestions, they would be much appreciated.