Because the model automatically updates to the sneaking model when in areas less than 2 blocks tall, the player model will almost randomly over-ride the swimming animation with the sneaking one because the height above the player is greater than 1.5 blocks and less than 2 blocks.
[#https://youtu.be/dsvwUXdamew|https://youtu.be/dsvwUXdamew]
Environment
64 bit operating system, Windows 10 (playing Java edition with most recent version of Java), 8gb ram on computer.
Duplicate of MC-148627