Apple has posted a support document about what you should do if your iPad Pro doesn't respond when you press buttons or tap on the screen, and the screen is black.
It’s pretty simple. Apple says that to get back to using your iPad Pro, force restart it by pressing and holding both the Sleep/Wake and Home buttons for at least 10 seconds, until you see the Apple logo.
Apple says it’s aware of this issue and is investigating. The support document will be updated as more information becomes available.