I reported this back in May with a screenshot, video, save and instructions on how to reproduce it in this post.
Since then I've noticed that this mainly occurs when the starting point and end point are not in a line along the hyperlane. If the two points form a straight line that is not on a hyperlane, the ship will follow the hyperlane for a while, then sometimes start moving directly towards the end point. Sometimes it will correct itself for a turn before doing it again. Other times it will follow the straight line instead of moving back to the hyperlane. This is especially bad when I have +500% moves. I now try to move ships in increments that are straight lines along a hyperlane to avoid the bug.