You put the loop in the wrong place, I’m assuming.
You put ONE ISM in total. Set the mesh. Then add lots of instances.
So, all your spline code goes AFTER you have added the ISM. Only the AddInstance part goes in the loop 
You put the loop in the wrong place, I’m assuming.
You put ONE ISM in total. Set the mesh. Then add lots of instances.
So, all your spline code goes AFTER you have added the ISM. Only the AddInstance part goes in the loop