GPS is not working when my iPhone is locked

[CJBoggs30]

Hello, I got an IPhone 15. And when I go out for my runs, I like to use the GPS feature on the app while wearing the Fitbit Charge 2. Although, I’ve discovered that the GPS tracking does not work when my iPhone is locked. Even if I lock my phone while on the Fitbit gps screen, the app creates a fake path due to not correctly tracking. 
Does my iPhone always need to be unlocked with the Fitbit app on while on my run for the tracking to work?

Moderator Edit: Clarified subject

[LZeeW]

Hello @CJBoggs30 and welcome to the Community.  I don't think that this has anything to do with your iPhone screen being locked.  Other users are complaining of this, too.  Fitbit calls this feature MobileRun.  I don't use MobileRun, but I did a test walk and it is happening to me, too.

I know that many users like tracking with the app because you can get voice cues.  There is another issue with MobileRun.  Exercise details list walk as the exercise, even if you choose run or hike.  MobileRun is a very old feature.  I don't expect a fix any time soon.

[CJBoggs30]

I appreciate the reply back. Yeah, it works when the phone is unlocked, it’s just when it’s locked it doesn’t read but creates “guesses” of where I went. 

Do you use any other apps to track gps for walks?

[LZeeW]

@CJBoggs30  I know many runners like using MobileRun because it gives you voice cues.  Do you get a correct map if you use the Exercise app on your Charge 2?  I use the Exercise app on my Sense 2 when I want GPS tracking.

Fitbit's newer devices have a 'Laps" feature that will give you vibration feedback at distance intervals, but can't give voice cues.   

I don't normally use the phone app for tracking.  I used it on that walk to reproduce this issue -- to be able to give feedback to Fitbit.