Fish sometimes stop moving

At some point, Tropical Fish, Salmon, and Cod simply stop moving and at best only spin around. This happens even if the player is nearby. The swimming animation however continues to play.

The video below shows how some of the salmons didn't move, but just spun around.

To reproduce

(from MC-208729)

1. Create a body of water of any size. I used a 8 x 8 x 5 box
2. Fill it with tropical fish (you want at least a couple schools, I did about 100 fish)
3. Wait. Some fish stop moving within a couple minutes. Within 6 or 7 minutes, most tropical fish will either be crowding into a corner or have stopped moving entirely. The larger fish seem to take longer, at least when densely packed together.