Apps, whether they're downloaded from the App Store or Cydia, can crash from time to time because of underlying bugs, and re-launching it will sometimes let you go about using the app without any issues.
If you use a particular app that seems to crash here and there, then a new free jailbreak tweak called AutoLaunch could be your next best friend. It can automatically re-launch any app that crashes on your device so you don't have to re-launch it yourself.