FYI – I am running into the same issue. Not sure if it is after hitting a certain length (my post is close to 10.000 words). I will try the new admin user trick.
To add some info:
I can revert back to an earlier version and the editor will load so I think the issue is a bug on how the shortcode is written. I keep reverting, moving forward, revert again, move forward etc etc. Next time it happens, I can post up the diff of working vs a non working version.

• This reply was modified 9 years, 9 months ago by cakesson.