@FriedOkra That’s probably caused by some of the spline points not having a rotation vector set to zero. To fix this select a closest point on a spline, go to Details Tab (Components view) -> Scene (Inherited) -> Spline (Inherited) -> Selected Points (Category) and make sure Rotation property is set to (0.0,0.0,0.0). Repeat for other points if needed.
@ambershee I think this bug appears when using Single(Legacy) mode. This mode was left only with backwards compatibility in mind and should not be used. It will be removed in the next update to avoid confusion.