Xcode 8 beta 6 core data error

I got it with Xcode beta 5 today.

It has been resolved after saving the coreDataStack context before performing a fetch request with a NSFetchResultController.

I'm having this issue as well, what does saving the coreDataStack context look like. Does this count?

(UIApplication.shared.delegate as! AppDelegate).saveContext()

I saw this recently. It seems that it didn't like the fact that I was creating a new child context and adding unsaved object to it before creating a fetched results controller and calling `performFetch`. Reversing the order of operations (set up FRC and THEN add objects) removed the errors. I didn't not have to save the new objects.