I think in thus case the issue is being caused by the shape of the base spline, similar to this recent post
. In your scene file I can see the spline has a few small kinks that are causing this problem.
Small deviations in the path like this can become magnified by the time they reach the furthest vertices. I'm afraid the only way to to fix this issue is to edit or recreate the spline.
I hope that helps but please let me know if there's anything else I can do.