Apple Watch not appearing to friends on "Find me" - only iphone

Hi

My son has an apple watch 6 (cellular) and an iphone. When we try to locate him on "Find My", only his iphone shows up and not his watch. When he goes into "Find Me" he can see all his devices including his watch, and when we call him, both his watch and his phone ring so it seems to be paired correctly.

In settings, "Find Me" - My Location is set to his phone and cellular Apple Watches. All location settings are set to share.

The first day he got his watch it worked fine but has just suddenly stopped.

I have tried unpairing and re-pairing the watch but it doesn't make a difference.

Can anyone help?

Thanks