As I understand it, there are some Apps that can add hooks into certain URLs that cause the link to open in the installed App instead of Safari (or other browser). If the database of App links was too big it could cause Safari to become unresponsive. Some popular travel App was one of the apps with too large a DB which the App developers fixed, but iOS 9.3.1 addresses the root cause.9.3.1 installing now ...
I wasn't affected since I didn't have that App, but upgraded anyway. It's been running fine for me.