The Blue Line is called the Railing Reference Line.
The green line is probably the Railing body itself.
The perpendicular distance of the Railing body from the Railing Reference Line is determined by the Reference Line Setting in the Segment page of the Railing Settings Dialog. It is probably offset to a distance to the left or right.
If the railing body is shifted at a distance along its length, that can be caused by one specific setting in my experience. In the Railing Settings Dialog, select the Node page on the left, and the check to see the value set in the Ending Node Offset field. If it is set to a non-zero value, this shifting can occur. Try to set to back it to zero.
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