Yeah, it happened to me. Connecting it to iTunes as recommended gives a dialog box that something was wrong and asks if I would I like to upgrade or restore. I selected Upgrade to 9.3 and it churned for a while, tried it and failed to activate again.
It was about 1 AM by then so I just selected Restore to 9.2.1 and went to bed. When I got up it was operational and I had to go through the initial setup stuff as usual. But when I tried to check for software updates, it said I was already on v9.3. Maybe that happened because I had tried the iTunes upgrade to v9.3 initially. Or maybe it's lying to me. Whatever. It did restore perfectly.
Unfortunately the old iPad 2 does not get Night Shift functionality, so I was sad again. :-)