Could you download the test project in this post, and duplicate some of those folders a couple of times, to bring it up to 1m words? The project is at about half a million.
If that loads Scrivenings successfully, your next goal would be to change any project settings to make it conform to how your large project is set up. Page view, line numbering, editor zoom, anything along those lines that would change how the editor functions. For the best results, I would recommend viewing one item alone, changing a setting, and then clicking back on Draft to see if that causes the problem, one by one. That way if it suddenly stops working, there is a high chance it is that one setting.