Find My leave and arrive notifications inconsistent on my iPhone

I live 300 miles from a family member.

We share our locations to each other so can observe each other’s location moving around in real time if we look at the app at the appropriate moment.

I have set up when I leave and arrive home to notify the other family member and it works fine

I have also set up from my phone when the other member leaves and arrives their home and they have accepted both.

However sometimes I get notifications from them and sometimes I don’t.

We have checked everything and can’t see why this behaviour is happening.

Note when they leave and I don’t get notified I still see their location ‘blob’ on the app move away from their house.

I don't have any DND or focus activity on my phone to account for the behaviour

I have iPhone 15 the other phone is XS and both are up-to-date with 18.4.

Anyone have any ideas why some notifications don’t come through?

[Re-Titled by Moderator]