If you switch to Imperial measurements the top speed listed in active track is 49Mph. Dji ****** up their math and each different measurement setting gives a different top speed. Stick with Mph for the fastest top speed.
It is a bug within GO 4.0.5 for Android which I now have reported to DJI.
I have tested yesterday again and taken screenshots.
Just compare these three screenshots. The only difference between is the Unit settings, either Imperial, Metric (km/h) or Metric (m/s).
As you can see the "Max. Speed Priority" value is not consistent. 49.2 mph converted results into 79.2 km/h and 21.9 m/s.
But when switching units, conversion goes wrong and results into 15 km/h and 15 m/s. And it seems as if this is not only a display problem but really limits Mavic's top speed! As I am usually selecting km/h that means that ActiveTrack is limited to 9.3 mph. I tried switching to Imperial today and then the Mavic got as fast as expected.