iPhone location sensor routinely fails to detect entering home geofence

**iOS device model, version and app version**

Model Name: iPhone XR
Software Version: 14.7.1
App version: 2021.216

**Home Assistant Core Version**

2021.7.3

**Describe the bug**

I have an automation setup that arms Blink when the last person leaves home, and disarms it when the first person arrives home.

I have found that around 40% of the time the disarm trigger fails because entering the home geofence is not picked up.

I've just been out and the iPhone sensor picked up that I was away. It still hasn't detected I'm at home now, though.

This has occurred in the last few versions - as far back as I can remember.

Full location permissions have been granted in iOS.