Is the spoke a little bent in the area that two spokes cross each other? As the sprocket is tightened it puts a strain on the spokes making the spokes tighter than they were when you begin the install. A bent spoke becomes shorter/tighter, if you know what I mean. From looking at the pics..two and three...that "X" is close to the rubber. I wonder if you should wait until the sprocket is installed before "truing" the spokes. I know this does not address the fact that it's always the same spoke but it's all I can offer.