Currently, devices with under 1GB RAM may experience issues with the game. Optimizing the game is one of our top priorities, so we hope to improve your experience in the days to come. At this point, we suggest you make sure your game is up to date, and not to have too many concurrent apps running with the game.
However, if you’re crashing in specific areas of the game (eg. the game always crashes when you try to upgrade), or if you suspect it may not be a memory issue, let us know through Chat/Help and we’ll be happy to help you!