It looks like there have been a number of reports of iPad Pros becoming unresponsive after being charged. Apple has responded to the tech support claims and is working on a permanent fix for the problem. In the interim, they offered up a temporary fix. A hard reset will fix the issue until it happens again.
The problem has affected multiple versions of the iPad Pro. Here's Apple's statement on the problem,
We will update you folks when a more permanent fix is presented.
In the mean-time, be sure to stop by our dedicated iPad Pro section for further discussion: iPad Pro Forum | Apple iPad Forum