Is your iPad in guided access mode?  If not, when someone hits the iPad home button the App will be minimised and the external screen will freeze. Follow the below steps to setup guided access: 

b. Scroll down to the bottom of the page and toggle Guided Access to ON (Green) – advised to use a Passcode for this which can be activated within these settings.

c. Please also ensure that Mirror Display Auto Lock has been toggled to ON (Green)

Note: if Mirror Display Auto Lock is not applied the iPad will automatically sleep after a period of inactivity, this will affect playback of classes.

We strongly encourage using a video EDID that supports audio extraction for the most reliable system. A video EDID will stabilize the connection between the projector/TV wall/display and the iPad. Some also provide the function to separate the audio and video channels so the audio from the Virtual app iPad can be connected to a separate audio system. Find out more through the link below: