Chance Miller, writing for 9to5Mac:

Apple, just hours after it confirmed issues relating to iOS 9.3 on the iPad 2, has released a new build of the operating system for the device. Carrying build number 13E236, the update appears to be rolling out to iPad 2 users now. Presumably, it’s the same build that was released to everyone earlier this week, just with the activation issues fixed.

From Twitter comments, appears that this new build addresses the problem.