Ever since iOS 11 came out, my iPhone 6s intermittently "freezes" or "shuts down". It's difficult to phrase it exactly, because I typically see some different behaviours:
- The phone freezes and is unresponsive, but it's still active (e.g. playing music). The screen is black and lock/unlock button is unresponsive. Frequently happens after pressing the lock button once, after which it will not respond to an unlock request.
- The phone suddenly "semi-shuts down". Music playing will stop suddenly and Bluetooth connections such as AirPods will be lost. The phone is either entirely black or "graphically black" with a spinning wheel for about 20–30 seconds. It does not appear to be a full shutdown, because no reboot is required (i.e. the Apple logo isn't displayed). The phone returns to the Lock Screen after the black screen or spinning wheel.
It should be noted that my phone has battery problems described here and here, which is to say that in iOS 10 the Phone would suddenly completely die at 20%. While the issue could definitely be related to the faulty battery, it does not appear to be similar, and these new shutdowns occur also at near-fully loaded battery levels.
Anecdotally, I don't have much to report other than that the Lock Button seems to trigger a freeze sometimes, but as stated above shutdowns can happen by themselves without any particular action by me (except streaming music).
Note: This problem did not occur in iOS 10 or similar versions with the very same phone.
Edit: I have not replaced any part of the iPhone, e.g. I don't use a third-party replacement screen. The iOS 11.0.3 update that was intended to address issues relating to replacement screens, did not help.