Black flicker when transitioning

Only on real device (e.g. iPhone 6) I get black left side of the screen when the view is transitioning to another one. It’s not always - it might be connected to poor performance as I’m downloading a lot of data on the background. It only started happening recently (but no lib update etc) - I only implemented app redesign.

BTW It’s not so much the black colour but why it’s happening and how to stop it completely.
Thanks for any idea

Cordova CLI: 6.1.1
Gulp version: CLI version 3.9.1
Gulp local: Local version 3.9.1
Ionic Framework Version: 1.3.0
Ionic CLI Version: 2.1.0
Ionic App Lib Version: 2.0.0-beta.20
ios-deploy version: 1.8.6
ios-sim version: 4.1.1
OS: Mac OS X El Capitan
Node Version: v4.4.5
Xcode version: Xcode 8.0 Build version 8A218a