Restart the app once.

On the iPhone
Close the app by double tapping the iPhone home button and swiping up on CMA. Reopen the app and it's good as new.

On the iPhone X
Swipe up to see the list of apps in the background. Lift up your finger so the apps are all visible, then tap and hold until the red button appears, then swipe up. It's actually easier to do then we could explain it in words.