When a curved segment of a path has diverging handles that are oriented in different quadrants across the X axis (this is my guess), like it’s shown in the attached document and the GIF, Illustrator renders the result only up to the horizontal tangents of the path. Same thing happens if you try to toggle Align Stroke options (they seem to use the Offset math).

Adding and extra point on the rendered segment helps, but it’s not really a solution.
The bug is quite old and perhaps it’s time to get it fixed?