The bug in question is noticed by the shape when swimming. Without the dolphin the player will swim normally. With the dolphin, the player will swim and feel a change in the fov , during the swim but without adding an effect to the effects bar, and without being able to activate it through commands. I can't sent a video because is too long ( 14.76 mb).
How to check the bug: First make sure you are in a place with water. Second Add the dolphin to the water and notice the change of the fov during the swim with and without the dolphin, and you will notice that "there is no" the grace effect of the dolphin.
Here is the link for the videos about the bug:
https://drive.google.com/file/d/1cZsJOZ5lrKCAgrEEVnYhoa0uWfRBMwbX/view?usp=drivesdk
https://drive.google.com/file/d/1cbHV4PC8N99UVInF5Dkkz3MnFUSSQkT9/view?usp=drivesdk