Basically, Puzzle Trooper holds the Diamonds in different wallets for the various platforms supported by the game. If you happen to switch between platforms (from any Android device to iPhone, for example), you will not have access to the earned and/or purchased Diamonds from your previous device, which is Android in this given example. Upon playing and you managed to earn or purchase Diamonds in your iPhone you will not have any access to the Diamonds again if you return to Android. In short, you will not be able to have access or combine Diamonds from two different platforms.
You can always return to your previous device or platform if you want to gain access of all the Diamonds left in a given platform.
If you want to know more about the term Platform, kind refer to the link Here.