GPS Issue with Cube Black


I am having problem with with my here+ gps used with cube black. I am installing cube black and here+ gps for a rover. I already did the calibration for the compass, and the red line( current rover direction) is always pointing at the right direction.

The issue is the black line( GPS tracked) which is always perpendicular to the red line. Is this normal?

When i try to put on an auto mode, the rover seems to be wondering endlessly. The red line and the black lines will always have a huge error and not merging as when i tried in the SITL mode.

Hope to get some help here

Many thanks