All data ok on OSD apart from home distance and direction

I have an APM 2.6 on a quadcopter which I fly FPV.
I also have a minimOSD.
When I start flying I have both the satellite lock and the GPS Co-ordinates on screen so I know the GPS is working, (I can fly auto missions no problem)
I start flying and the battery voltage and altitude are also displayed correctly but the distance to home and the home direction arrow, although displayed, don’t work.
The home direction arrow does not move and the distance to home always reads 0m.
During the flight if I switch to RTL the quad flies back and lands itself as it should so it knows where home is.
Any ideas what is wrong please?