Game stuck and crash while playing

I have 2 problems in my game when export to Window Phone (I run on Lumia 525).

First, It has a Main Menu and 3 level. When I go to level 1 => go back to main menu => go to level 2 or 3, and now, game screen display the scene of level but it's stucked: I cannot control the player, the camera also freeze at current position but music is still played. This issue rarely appear, only when I change level too many times (level 1 => main menu => level 2 => main menu => level 1 => main menu => level 3 ...etc).

Second, sometimes, while the game is running, it's crashed suddenly, the app is closed and exited to home screen completely.

How can I fix these problems ?

Thank you.

PS: Sorry, I'm not a native English.