Crashing

This morning I was working on a custom chart and noticed it started lagging after a short while. I'd crash 20-30 times after finishing just one song. I've cleared my phone's memory and the game's cache, and even restarted my phone, but it still happens. My phone isn't overheating either, it's just warm. When playing songs, completing quests, or playing mini-games, my phone gets extremely hot but has never crashed.