A common observation with the more credible sightings is that they move back and forth like a ping ping ball without a change in velocity. Same goes for 90 degree turns, and I don't think that part is receiving enough attention.
I think that they're using a 1d border between 2d planes like a zip line or a railroad track. Here's my logic. If one travels to the end of a 1d plane, the only possible outcome is a 90 degree turn or a course reversal. Same thing that happens if you drive to the edge of the universe at ftl speech. Space itself will turn you around without a change in velocity or g forces because it's the plane itself that is " turning" and your velocity relative to the plane remains constant. Thoughts?
A '1d plane' is actually a line and doesn't have an end, it's an infinite.
But changing direction along that line would not appear like a 90 degree turn in our 3d space any more than a train going back and forth on a track appears to make 90 degree turns. I'd also add that changing direction does not inherently have to seen instant.
I think the more likely explanation is that they're controlled by a controller, and it has four directions on it.
It moves in the way that a data travels through the circuits on a motherboard