As you see in the pics, the unit has only 2 movement points per turn. but, it will move 3 tiles after 2 turns while passing over AMBERGRIS resource that has 2 movement cost of its own.

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Save game: Babylonians Turn 62.ctr

For an unknown reason, this particular ambegris tile is not generated correctly and is "freely" passed (without movement cost) by your transport galley. The tile's tooltip even says that you need 2 movement points to pass through it. 

But the autopathing doesn't calculate these movement points : starting from the reefs tile below, you'll go through the ambergris tile freely.

Once on the ambergris tile, the transport galley's movement points are still 2, and from this point, the correct autopathing applies.

Meanwhile, the other ambegris tile (on the west coast of your continent) is properly generated (costing 1 movement point) and doesn't mess with the autopathing :

I guess it's a map generation bug on this particular tile, something I've noticed lately with the current build. I shall make a bug report too if I encounter them again.