iPad air2 keeps turning itself off.

The battery is showing at 100 % and there are no signs of overheating at all. No updates waiting and is currently showing at version 15.8.3.

Sometimes it’s while I’m using it, but also does it after not using for a few hours . . I pick it up to use it after it working fine previously and it’s turned itself off. It’s really hard to force it back on again and when I do, it will stay on while it tries to configure the apps but 9 times out of 10 will turn itself straight back off again. It means I’m spending about 30 mins just trying to get it to come on and STAY on. I’ve tried getting rid of unused apps or photos etc, but it doesn’t make any difference.

Does anyone know what may be causing it ?