Frequently, the game locks up on me (like 3 out of every 5 times)

The game freezes and nothing can be clicked.
Pressing the iPhone home button takes 30 seconds or so to respond
Once App exited, double tapping to bring up task manage or swiping is also unresponsive.
Once I kill the MW App, the phone works again perfectly.

I've noticed that the App Size has grown to 1.8GB on my phone also.

Has anyone else experienced this/Know a solution ?

Cheers,
Ro