Fénix 6: km notifications on run different to distance on watch face

The last months the km notifications each km do not match the km distance logged on the watch face. 

at the end of a run it is the watch face distance that is logged and I think is correct. Eg today 14km via notifications but 12km on watch face activity tracking. 

I have used this for a few years and this has never occurred before. 

any ideas how to resolve?