iOS 11 and GPS accuracy on iPhone (6+) GPS on my iPhone 6+ has always been accurate. Amazingly accurate. Most of the time, it took only a few seconds to pinpoint my location on any app using GPS, Apple Maps, Google Maps... This has been the case for almost 3 years.

Update to iOS 11, then up to iOS 11.2.1

After the update to iOS 11 / 11.2, GPS is never accurate. The best it can get to is an approximate location of a radius of 20 meters. And often, the actual location is even outside that circular area. Whatever the app, same problem.

Tried to go in a very opened area, with no building, no trees... on a very blue sky day. Waited for minutes in Maps... same problem.

Tried the common fixes found everywhere on the Net


Reset Network Settings (after each update, then have to enter all wifi passwords again)
Reset Location &amp; Privacy
Location Services ON/OFF
Reboot ... several times
All apps have been updated to the last version (eg Google Maps)
Airplane mode ON/OFF ... 
and of course, tried with wifi ON and OFF


Nothing has improved in the GPS department...

(Unfortunately cannot restore to iOS 10 since I don't have a fresh backup of before the update)

Is this a known issue for some iPhones (namely the 6 family)?

Any other advice welcome.

edit 

No improvement with 11.1.2

Nov 28 update

As of today, everyone I know who has an iPhone 6+ on iOS 11+ and use GPS a lot has this problem. Did an app to calculate the best accuracy the device might have within 30 minutes, under a clear sky, out of town - GPS is always erratic, inaccurate. It's definitely an iOS / firmware issue.

Went to Apple store and talked an hour with the manager, explaining the problem etc... Basically answers were


  
  there is nothing to do - your phone is defective and has to replaced with a new/used one [buy a new [678]+, or an X]  ...
  


Dec 22 update

It seems the reason to this sudden trouble could well be due to Apple slows down iPhones as they get older. GPS is a complex mechanism, and forcing the CPU (and other components) to act differently, to slow down, and probably get less power, could have an effect on the GPS chip and behavior.
Try updating to iOS 12. This should hopefully provide a fix for it. Also when you try to get your location try to wait a bit as accuracy improves over time. Make sure that you've set the date, time, and time zone correctly on the device in Settings > General > Date &amp; Time. If possible, use Set Automatically.


  GPS accuracy depends on the number of visible GPS satellites. Locating
  all visible satellites can take several minutes, with accuracy
  gradually increasing over time. To improve GPS accuracy:
  
  
  Make sure that you've set the date, time, and time zone correctly on the device in Settings > General > Date &amp; Time. If possible, use Set
  Automatically.
  Keep a clear view in several directions. Walls, vehicle roofs, tall buildings, mountains, and other obstructions can block line of sight
  to GPS satellites. When this happens, your device uses Wi-Fi or
  cellular networks to determine your position until the GPS satellites
  are visible again.
  


(Source)