Apple has introduced new changes to their operating system iOS version 12.
One of these changes has an impact on your Vizito app.
By default you might have your iPad go into sleep mode after 20 minutes.
However there's an easy fix for this by configuring the following 2 settings for iOS 12:
General > Accessibility > Guided Access > Mirror Display Auto-Lock > ON.
and Settings > Display & Brightness > Auto-Lock > Never.