When you create a Clip (a section of the model) and create a vector arrow part from on the clip, you will have one vector arrow starting from each node. If in your geometry you have degenerate nodes (i.e.: multiple nodes at the same location), you will get multiple vector arrows starting from the same nodes.
To avoid this problem, you might want to create a grid clip plane. When using the grid option for the clip plane, EnSight will do a re-mesh of the section cut. This re-meshing will ensure that you have a set of nodes equally distributed.
You can find a more detailed description on the steps to follow at this FAQ: