I had two of these refurbished iPad with same issue. Here is what I did to fix & also avoid it from happening again. ———- This is how i fixed my ‘existing, problem: - Put off Bluetooth from ‘Settings’ ONLY and not from the quick menu. Go to settings—->Bluetooth —> off. Repeat this process twice. ON/OFF, ON/OFF. Do this process super ‘promptly’ as soon as the ipad turns on. IF THE IPAD SHUTS DOWN BEFORE PERFORMING ABOVE MENTIONED ACTION. ? Then, Connect the iPad to charging and then turn iPad on. Then perform the settings->BLUETOOTH action. It won’t turn off when plugged in. This is what I did to “avoid” it from happening again: -Best & Permanent solution for me was — before plugging iPad into charging, ALWAYS turn the Bluetooth OFF. -Not to put iPad into charging with ipad off. iPad should be ON while it is charging. This is the only thing that worked for me. Hope this might work. Worth a shot. Thanks.

iPad Pro Shuts down when charged to 100% SOLUTION FOR ME- once ipad is charged 100% a- enter your passcode as usual if locked—- FIRST thing, put it onto AIRPLANE MODE, put BLUTOOTH OFF and even put off WiFi if possible and use ipad for 2-3 minutes. Then only start using ipad with Blu-tooth, cellular or WiFi functions. (IMO might be, as soon as the system starts, -it tries to hit blutooth or cellular functions and this might be impacting the battery function)