It seems using lots of blueprint in my project was a mistake, because there’s little guarantee things will continue working in future versions and once UE4 decides it doesn’t like your Blueprint you’re SOL and all work put on it is lost.
One of the many different crashes I’m getting in 4.6.1 was caused by a few NULL nodes in a blueprint graph, which means some nodes got “eaten” during loading for some reason.
If I make another UE4 project, I’ll be sticking with C++ for as much as I can possibly manage.