iPad turning off for no reason

My IPad Air3 has taken to just turning off for no apparent reason whilst I am using it. This happens if the battery is 100% full or 10% or any number in between. It cannot be restarted and has to be left for varying amounts of time. I have tried plugging it into power but it still does not respond.. Tried all sorts of recommended button pressing but does not turn it back on. I am not sure if it is related to the recent OS upgrade now at 14.6 or if it is a hardware issue. Taking it to Apple is not an option at the moment as we are several hundred miles away from a Apple Shop.

Any suggestions?