Apps stay running in the background and can get into a bad state. Force-closing fully quits the app so it starts clean next time you open it.

On iPhone / iPad

  1. Swipe up from the bottom of the screen and pause in the middle (on Home-button devices, double-press the Home button). The app switcher opens.
  2. Find the misbehaving app’s preview card.
  3. Swipe the card up and off the top of the screen.
  4. Go back to the Home screen and open the app again fresh.

On Android

  1. Swipe up from the bottom and hold (or tap the recent apps button — the square or three lines). The app switcher opens.
  2. Find the app’s card and swipe it up (on some phones, sideways) to dismiss it.
  3. Reopen the app from the home screen.

Tip (Android): the thorough version is Settings → Apps → [the app] → Force stop. This is more forceful than swiping it away and works even when the app switcher is being difficult.

Still misbehaving?

  1. Restart your phone (Android).
  2. Check for app updates.
  3. On Android, clear the app’s cache.
  4. As a last resort, delete and reinstall the app.