iOS: Can't compile CoreData model because of Fetched Indexes in Xcode 9

I just ran into this issue in the Xcode 9 GM. What I observed was that unchecking the Ascending checkbox in the index editor caused this error to occur (it was only showing up after I made a new index). I am assuming that adjusting this index attribute is only supported in the iOS 11 fetch indexes (you'll notice any index you made prior to Xcode 9 are listed as ascending by default).

TL;DR: Make sure the Ascending checkbox is checked for all properties in the fetch index editor.