If you are shooting RAW + jpeg then there will be a 3 to 4 second delay whilst file is processed and written to card, before the button is available again.
I can try and do a video. It would appear that the lock in the upper right is relevant. I believe that is Auto Exposure. But my experience has been inconsistent. if I tap the screen first I get a higher % of functionality. But not 100% if I use the shutter key on the ipad I get 100%