iPad stuck in reboot loop.

As you have already sought assistance directly from Apple Support, it is very unlikely that anyone here might offer insight that has not already been covered by the Support Team.

Assuming that you don’t bemoan repetition of advice already given, you might attempt a forced-restart of the iPad:

• On an iPad with a Home button: Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.
• On other iPad models: Press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the top button. When the Apple logo appears, release the button.

Note: If iPad still doesn’t turn on, or if it gets stuck during start up, see the Apple Support article If your iPhone, iPad, or iPod touch won’t turn on or is frozen.

Restoring to Factory Settings may also help - recognising that you will need to force the iPad into its recovery mode:

Restore your iPhone, iPad or iPod to factory settings – Apple Support

I suggest your next port-of-call is either the Genius Bar of your local Apple Store, or Apple Authorised Service Provider (AASP), where the technicians are able to test, assess and hopefully resolve the issue.