Thanks for the question. Generally this occurs when using Clipping Splines
in combination with Extend X/Y Size to area.
RailClone's A2S generator builds a seperate square area that's large enough to encompass each clipping spline, and in some situations this can cause it to overlap an adjacent area. In this case it looks as though the problem is caused by the fact that the style rotates the array by 45 degrees and the corners are encroaching on another clipping area. The diagram below shows the reason for this issue.
There are two solutions. Either separate the splines into two objects and use a separate RailClone object for each one, or turn off Extend X/Y Size to Area
and set the size of the array using numeric values and position it so that it covers both splines, you can then apply the clipping as usual.
I hope that helps, please let me know if you have any further questions.