Is it possible for this case? When you download an App from App store, this App works well for a long time. But it doesn't work suddenly for some reasons. It must need you to re-install it and It comes back after re-installation.
There's no way to give a blanket answer to that scenario. Depending on what the problem is, there could be a number of solutions, from just restarting the device to having to remove the app (which also removes settings and cache files which are often the problem) and reinstall.