iPad Mini：Swift-App在低使用率时接收内存警告

i have a problem with my iOS-App programmed in Swift. I programmed an app which play different content types (Video, Image, Websites) in different views. But after a short time i run the app, the app receive a memory warning, but the memory usage of my app is about 20mb. So there is no reason for this memory warning. After a while the app crashes. Is it a bug from Swift, my iPad or anything else? I add a screenshot of the memory usage:i have a problem with my iOS-App programmed in