That’s a good question that no one, not even Apple, can really answer. What’s clear though, is that it happens quite often to many iOS users. In fact, it happened to my iPhone 6 a bunch of times since installing iOS 9 betas, but I thought the unstable iOS 9 pre-releases were to blame for the restarts.
Apple has a support page up for the issue telling users that they may indeed encounter unexpected restarts.
“You might see this unexpected behavior on your iPhone, iPad, or iPod touch if you have an older version of iOS,” Apple’s support document says, advising users to keep iOS updated to the latest version and also to update all their apps.
If that doesn’t work, then you should contact Apple Support or check a different support document if your device won’t boot past the Apple logo, or won’t respond.
If you ask Siri why your iPhone keep restarting, you won’t get a real answer. “An excellent question,” she might reply, without providing any actual help.
Meanwhile, as Gizmodo points out, many iPhone and iPad users are sharing their “iPhone Keeps Restarting” grievances. In fact, there’s a whole Tumblr blog dedicated to the matter, and you’ll find plenty of tweets regarding iPhone restarts as well.
“Put your hands up in the air if your iPhone keeps restarting outta nowhere, “ one user said on Tumblr.
Gizmodo also points out that an innov8tiv article contains a bunch of unofficial fixes for the issue, “a hodgepodge of ideas like turning mobile data on/off, resetting or restoring your phone, deleting ‘bad’ apps, and more.”