Some photos missing geotag

I've been taking photos on an iPhone 12 mini running iOS 15.6 using the default camera app. I've enabled saving of location data with photos. I've noticed that location data is being recorded for some, but not all of my photos, without changing any of the settings between taking photos. Why are some photos not recording the geotag?

I've thought that it could be either that a GPS fix couldn't be obtained at the time the photo was taken (e.g. not enough satellites detected) or a difference between whether photos were taken when logged into the phone vs when the phone is locked (e.g. camera opened from locked screen). Thanks for any advice!