It fixed a problem where users' Apple Health data were being deleted. As soon as it was installed, activity, sleep and nutrition records were lost and reboots or factory resets do nothing to bring it back. But when you fix one thing, you end up adding something worse.
Even stranger is what happens when you plug it in to charge it since you assume your iPhone's completely out of juice. It will show it's at 30% again after you restart the phone! You can unplug it and it will have the 30% charge as if it was supercharged within the time it took to restart your phone.
6. Even Weirder Charging Problems, According To Users
Some people have found stranger things happen with their iPhones post-iOs 10.1.1 update. In a thread found in the Apple Support Community forum, one user shut down the phone at 80% but couldn't start it in the morning because of the 30% battery problem. It only turns on when plugged in again...at 30% of course.
Battery power in an iPhone can be affected by many reasons, and there are ways to fix it. Active and background apps drain power, so synchronization plus Twitter can lead to less battery life. Overheating also does a number on your iPhone's battery.
A good drop on the floor has also been known to start battery problems as well. Many users on the forums also say that their battery drains faster after they drop their phone. It'd be a bummer if you haven't upgraded to 10.1.1 only to realize that bump from last week is the culprit to your battery-draining woes.
Users have not been having luck fixing the problem. Re-installing the upgrade does nothing, as does upgrading to the iOS 10.2 beta. The 10.2 beta only fixes the battery drain, but will still shut down.
10. Here's Some Options You Can Use If You're Affected