iPad Air 4th gen keeps restarting automatically

Whilst holding iPad In a folio case, it keeps shutting down. Other times the battery level drops from (eg) 80% to 1%, then I have to restart it. I have used the iPad on battery and connected to power. I’ve done a Factory reset and also full reset, connected to Mac. This caused the iPad to keep shutting down whilst setting up the iPad. 

Is this a known issue? What can I do to ensure this issue stops happening?