There is a known issue involving interrupted Airplay playback and the auto-lock mechanism built-in to iPhones and iPads.
When this auto-lock occurs during your Grokker video it can cause problems staying connected to Airplay. You may not know you have the auto-lock enabled so follow the instruction below to see settings for your device:
Select Settings on your iPhone or iPad > Select General > Select Auto-Lock > Set to Never
Auto-lock preferences may be reset when you update your OS so if you experience problems with Airplay after upgrading your OS check the auto-lock settings.