The most recent updates to iOS (8 and 9), along with the new resolutions available in the latest Apple devices mean that Word Games is not compatible with all devices at the moment - this might mean it doesn't run on the device at all, fails to use the full screen, or suffers other problems.
We're working on an update which will bring it back up to date so if you've updated your device you'll still be able to get your daily Word Games fill!