This may be an axial fan thing.
maybe there is a sweet spot where the velocity profile is flatter
The flow should normally have settled by 60 cm, so it may be making a vortex in the tube.
I think a diffuser is necessary to even out the flow velocity profile.
Anyways, using the anemometer software calculation of the averaged traverses I got 5.24 m/s at the outlet and 4.98 m/s 15 cm from the outlet end, through a clean hole. The hole traverses also had the high flow at the pipe edges. These are my first two averaged traverses, so at least they are showing nearly the same value and that value itself seems possibly about right, even with the weird flow distribution.
(These anemometers really could use a ruler built into the head since there is no way to look how far exactly the probe is in the hole in order to perform a proper traverse.)