First kilometer "too long" without GPS

When doing my normal run with GPS enabled, this comes out around 5.5 kilometers, 37 minutes and 6176 steps. When doing the same run without GPS, and with the running step length set to 83 centimeters, the results used to be about the same.

However, since a few weeks this has changed and the total distance for the same run now varies between 3 and 3.5 kilometers, but with the correct number of steps and time. The major difference being that the first kilometer is not "clocked up" until after about 2 kilometers. I have tried to do a reset but no change.