It appears that this issue has come back: CollectionView's selectedItem / selectedIndex does not work
In my itemCollection, when I select an item it properly sets the selectedIndex, but the selectedItem is still null. I've built my app based on the selectedItem behavior and it currently is broken.
Hello @Milo_Watanabe1!
Thank you for surfacing this. I just found out this bug has been reported but there is a workaround.
The selectedItem property will change if there is an event handler.
If you don't want any behavior on click, you can add event handler to the collectionView that runs a script that does nothing 
I know this sounds silly but once you add the event handler to the collectionView it will properly update both!