I had some of my ships moving a long distance using hyperlanes. Occasionally, they would leave the hyperlane and move out into the regular tiles of the galaxy. There was no reason for this. There wasn’t anything in the hyperlane that would block them or slow them down to make the "bad" path better than the intended path
I happened to have a save just before I saw it happen with two different ships as well as with a fleet. In all three cases the ship or fleet traveled along the hyperlane for a while before changing direction to move away from the hyperlane. One would move away until it ran out of moves. Another would move away for a few tiles before reversing direction and heading back to the hyperlane. It would run out of moves just before it made it back to the hyperlane. The fleet would leave the hyperlane for a while, then would hesitate like it was wondering what was going on, then it would begin heading to a different hyperlane that was close to it. In all cases they were originally showing their paths would always stay on the first hyperlane.
I have a video showing this and a save from the turn just before it happens. A zip file containing them, a screenshot and a text file with detailed instructions on what to do and what to look for is available here.