Lily accuracy

Some months ago I bought a Lily watch for  my girlfriend. Since the start the accuracy of measuring distance is way off.

It happens that my fenix 7 shows 5km and hers 7km. The lily always shows more, but strangely when looking at the gps map drawn in the app it seems to show on both exactly the same route?

So why is the distance measuring so off? Why does the lily not correct itself by looking at the gps data?

I have doen multiple tests, even with three garmiin watches (fenix7, 6 and lily) in where the fenix 6 & 7 where close (100m difference on 12km) but the lily had a huge difference in distance.

So how can this be fixed?