Axolotls keep stopping and treading water for ages, especially in shallow water

Axolotls frequently stop and tread water for ages, bobbing up and down in place, before moving off again. This is particularly true in shallow 1 or 2-block-deep water, but can also happen in deeper waters, such as in rivers. It happens when they come into contact with a solid block at the bottom of the body of water, they just abruptly stop swimming for 10-15 seconds. They can even get stuck in a nook because of this bug as they are unable to turn around.