Apple has released iOS 10.1.1 for iPhones and iPad, less than a week since the iOS 10.1 update which included iPhone 7 Portrait Mode. The bug fixes a specific issue with the Health app, where data was not showing for some users. There may also be improvements to other niggling issues, which are alluded to (“bugs”, plural) but only the Health fix is explicitly referenced in the release notes.
The update is available for iPhone, iPad and iPod touch users. To update now, hit Software Update in Settings on an iOS device.