I just downloaded an app update for the Hyatt mobile app for Android. I believe the iPhone update for the app has been out for a few week now.
From what I’ve noticed, it’s a very useful update. Prior to this update, the app was only great for checking out current reservations. It sometimes wouldn’t remember your login so you would have to log in every time you opened the app. Searching for, let alone booking, reservations (paid only) was a pain and easier done on an actual web browser.