IOS Find my friends, 'no location found'

[WarrenB]

We share our location in our immediate family with the 'Find my' app on iPhone, it's all working fine except for one phone. Everyone else's location is visible and working fine on this phone, but for some reason this phone doesn't show up on anyone else's, just get 'no location found' after a minute or so.

It hasn't been set up any differently from the others, all the permissions are exactly the same but it's still not showing on any phone. It's running the latest update of IOS 13 too.

We've tried setting it up again, removing and reading permissions and all that, still no joy.

Any not so obvious ideas we can try?