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Summary:
(context: See example project)
Sometimes, depending on the CoreData model configuration, when accessing the `groups` relationship on the `User` entity, we get `Story` objects although the target-entity of the `groups` relationship is `Group`.

Steps to Reproduce:
1. Open the attached example project and run it. Wait for a few seconds for the initial user object and groups relationship to be set up and the first story object to be added (Log message: "Added a story").
2. Kill the app (either on the simulator or by hitting the stop-button in Xcode)
3. Run the app again. After another story was added the Assertion in `CoreDataChecker` in line 44 will be thrown. It ensures that objects return via user.groups are actually `Group`-objects which is no longer the case.

Expected Results:
The `groups` relationship should always return `Group` objects.

Actual Results:
The `groups` relationship contains `Story` objects.

Version:
iOS 10.0 (14A345)

Notes:
In the attached configuration of the data model the `User` has many ordered relationships but only one unordered relationship. In the attached configuration the `visitors` relationship is unordered.

However, it does not matter which of the relationships is unordered, as long as exactly one relationship is unordered but the others are ordered the issue exists. 
* If all relationships on User are unordered, the issue does not occur
* If two relationships on User are unordered the issue does not occur

The issue only appears on iOS 10: copying over an sqlite-database that creates a crash on iOS 10 to an iOS 9 simulator does not result in a crash (using the same data model).

There are some more comments in the code about things we tried:
* Adding stories on a background context instead of on the viewContext does not seem to provoke the issue
* Adding stories to another relationship with target-entity `Story` does not provoke the issue, only adding the to the specific `stories`-relationship provokes it, even though the relationships seem to be identical except for the name.


Note about the project: 
* We tried using both the "old way" of setting up a Core Data stack + mogenerator generated classes and the "new way" via NSPersistentContainer + Xcode generated model classes. Both have the same issue.

Configuration:
any simulator or device we run it on had the issue

Attachments:
'CoreDataFetchesWrongEntity.zip' and 'additionalNotes.txt' were successfully uploaded.