iPhone 8 screen will not turn off automatically when not being used

Hello and welcome to Apple Support Communities, derekfromcoleraine.
If I understand your post correctly, you have to manually press the Sleep/Wake button to lock your iPhone as it is not automatically locking. I'd like to help.
Let's take a look at the setting that can affect this feature. Tap Settings > Display & Brightness > Auto-Lock and see which amount of time it is currently set to Auto-Lock after. If you have Low Power Mode enabled, Auto-Lock will be automatically set for 30 seconds. For more information about Low Power Mode, see this article:
Use Low Power Mode to extend battery life on your iPhone
Let us know if that resolves this issue for you.
Thanks for using the Apple Support Communities. Take care.

I had the same iaaue. I have tried these steps but it doesn't help. After that i have hard reset the phone, following these steps:

1. Press down and quickly release the Volume Up button
2. Press down and quickly release the Volume Down button

Now pass and hold the side Power button, continue holding until you see the Apple logo  on screen

After that everything is ok! Now it auto locks after 30 seconds as i have set it up. Hope this will help you!

Did this work for you? I have changed the settings as suggested, but still have the issue that the iPhone 8 will not auto-lock. I set it for 30 seconds, 1 minute, etc. Regardless of the time chosen, the iPhone will not auto-lock.

Yes, adjusting the timeout and restarting the phone worked for my wife's phone - however 2 weeks later it started doing it again. So I've repeated the process and it works - but this isn't a great solution.

Her previous phone on ios10 did not do this.

I wonder if restoring a backup to the new phone is a potential cause? But you should be able to restore a phone to preserve all your settings as that's why you buy an iPhone (for convenience)

Apple please investigate this - it's annoying.

I've tried submitting a bug report to Apple, however I wasn't able to include any log files as the phone has been rebooted to overcome the security implications of the problem - so I will have to wait until next time.

Possibly someone who next gets the issue might be able to nab the required log files.

https://bugreport.apple.com/web/?problemID=35503884

At this point, I haven't seen the problem in a long time. I've done the following since "the fix", so who know which of these has taken care of it.

1. Restarted the phone (hold power button until power off slider appears, wait a few secs, press power to turn back on)
2. Updated from 11.0.2 to 11.0.3.
3. Updated from 11.0.3 to 11.1.
4. Updated from 11.1 to 11.1.1.

For those who are still experiencing this problem, it's probably worth getting updated and restarting. If you still see a problem after that, report the bug to https://bugreport.apple.com. It's fairly useless to complain to Apple in the forums.

I have this issue as well, I have to restart it about every 10 days to get the function back. It's very annoying considering the cost of the phone and the fact that it's obviously not an isolated incident.

Same issue for me, too. I've had my phone for about 2.5 weeks now (8 Plus), and I noticed a few days it ago it had started to do this. I just now restarted and now it seems to work again, but this is very concerning, especially after reading the other comments about how it appears to be a recurring issue after every 10-12 days. Obviously, a major security issue, and I hope Apple will come up with a solution.

Update --> if you have an apple watch!

When i get a missed call, the alert keeps on disappearing and reappearing on the iPhone display. This kept the display turned on.

However when i dismiss the alert on my apple watch, then alert disappears from my iPhone too. This seems to have solved my problem.

Perhaps (generally) the updates going between the iPhone and watch keep the iPhone display turned on?

Hope this helps :-)

Given this seems to take about 2 weeks to re-emerge I think it's a bit premature to conclude the latest update (11.1 is only out a few days) has fixed it.

I hope so (and that it hasn't broken anything else ).

Yes, the same problem for me since I got the update on iOS , I restarted to fix the issue but the problem still exists. When contacted apple chat support they were ready to do all basic troubleshooting but I was fed up already about that process. Recently I raised 2 more bugs, one cracking noise, speaker issue when you keep full volume the touch screen will feel like vibrating when you touch and call drops without signal issue.

I have the same issue and restarting fixes it for a few days and then the process starts again.

I see that the answer from apple says that they have solved your original question does that mean they are not looking into this anymore and assuming its fine?

This is not a solved issue.

This issue keep occurring after a few weeks and the phone has to be reset again.

This NEEDs to be fixed by Apple ASAP it’s a ridiculous Either IOS 11 fault or IPhone 8 fault

Agree.. this issue is not solved as 3 of my family’s 4 iPhone 8s have this issue.. Restsrting the phone temporarily fixes it for a few days but it keeps coming back... as others mentioned this is a huge deal for people with sensitive data on their phone.. I can legit get fired for leaving my phone unlocked

Hi - can you confirm if this also happens with the latest ios 11 update (11.1)? I haven't noticed it yet with 11.1 but it normally happens after a few weeks on my wife's phone - so its not been out long enough for me to conclusively say.

What version of ios do your phones have? I think I did see it with 11.0.2.