Note: this bug also affects any custom mobs that use behavior.move_to_water

Steps to reproduce

1. Load move_to_water.mcworld. It contains a long canal along which are test areas for this bug (grassy end) and MCPE-165109 (muddy end). The lever on the command block at the middle of the canal toggles the canal between 1 block deep and 2 blocks deep. The row of command blocks at each test area will spawn a dolphin, an axolotl, a baby turtle, and a pregnant frog. (Note: the frog spawns with the components for pregnant behavior, but not the is_pregnant bit, so it will not create frogspawn.)
2. Set the canal to 1 block deep.
3. Press the button on the command blocks at the grassy end of the canal.
4. After a minute or so, toggle the canal to 2 blocks deep.
5. Press the button on the command blocks at the grassy end of the canal, again.

Expected result

After both steps (3) and (5) the mobs all start moving toward the canal within a few seconds.

Observed result

After step (3) the turtle freezes and the other mobs move randomly. After step (5) the axolotl, baby turtle, and pregnant frog move toward the water. The dolphin has an overriding issue reported at MCPE-181125 and can be ignored until that is fixed.