It appears that the scenario file for 'To the Rescue' on easy difficulty got corrupted somewhere between final testing and upload to AppStore. All other scenarios are fine. A fix for this issue was submitted to the AppStore, but due to Apple's review policy, it will take at least a week until it is available.
Sorry for the inconvenience and many thanks to Aaron, who informed me about this issue.
-- update --
The Apple was really quick this time, and an update to version 1.3.1 containing just the fix for this issue is now available on the AppStore. Enjoy!