Why does iOS kill the app (termination with signal 9: Killed: 9) when the iCloud switch changes?

Question

I implement the main features of iCloud. I track changes with NSUbiquitousKeyValueStoreDidChangeExternallyNotification.

Whenever I try to turn on or off the switch located in iOS iCloud Settings for my application, my running application is killed by the OS. This is not a failure. Here is what I see in the device log:

com.apple.launchd[1] (UIKitApplication:com.myApp) <Notice>: (UIKitApplication:com.myApp) Exited: Killed: 9
backboardd[30] <Warning>: Application 'UIKitApplication:com.myApp' quit with signal 9: Killed: 9

What could be the problem? Since there are no errors, I cannot understand this.

Can you share your experience, I will be so glad.