The iOS 10.1 update fixed a lot of stuff, but it caused a major problem for some users of the Health app: data disappeared in some cases, and even resetting phones and restoring them from fresh backups wouldn't bring it back.

That's the problem that today's iOS 10.1.1 update fixes—it's available now for all devices running iOS 10, including the iPhone 5 and newer, the fourth-generation iPad and newer, the iPad Mini 2 and newer, both iPad Pros, and the sixth-generation iPod Touch.

Apple has told us that the update should restore "missing" health data as well as prevent future data from disappearing. If you've been having this problem since you installed iOS 10.1, you should install the update as soon as you can.