If you migrate your data to a different operating system, you will not be able to transfer your gems to your new device. This message is displayed on the screen before you enter your transfer ID and password. If you have lost gems during your transfer, we are unable to add them back to your account. This includes migrating from an Apple device to an Android device or Amazon Fire device, an Android Device to an Apple Device and Amazon Fire device or an Amazon Fire device to a standard Android device or Apple device.
Please see the About Data Transfer section of the Help menu, which can be founds under Menu > Transfer > About Data Transfer.