App Freezes

If Realar smartphone App "freezes" - for example during Surface Plane finding the red square (or diamond) stops moving - the a quick restart of the App usually works. 

Steps to "force close" and restart an App:

iPhone 8 or earlier
Double-click the Home button to show your most recently used apps. 
Swipe right or left to find the app that you want to close.  
Swipe up on the app's preview to close the app. 

iPhone X
From the Home screen, swipe up and pause.
Firmly touch and hold the app, then tap [red] "-" . You can also swipe up to close the app as soon as you see [red] "-".

More information on How to force an app to close on your iPhone, iPad, or iPod touch: