I was getting some chickens to follow me home in survival and it seams once the mobs enter water they struggle to move forward to follow you. The same happened with cows and sheep. I will do some tests to work out what is going on and then post an update with the results.

Update:

• Friendly mobs follow into water and swim but move very very slowly forward.
• Friendly mobs on leads get dragged through the water.
• Friendly mobs occasionally stop swimming and then drown, usually when trying to get out of the water but can't even though it is possible. (I am aware this has already been reported).
• Hostile mobs don't seem to struggle with swimming when not following anyone. (Creepers and zombies tested)
• Hostile mobs struggle to swim forward when following player. (Zombie, Creeper and Spider tested) The spider was the best at swimming.
• Zombies Struggle to follow villagers if the zombies are swimming and the villager is on ground.
• Equally Villagers can't swim away properly if they are in the water and the zombies are on the ground.

All Tested in setup shown in photo. When working with friendly mobs i removed the end fences to give more space to get them to follow.

Update 2:

Results are the same with different depths of water. (tested depths: 1, 2, and 3)

Another thing is when chickens follow me they struggle to jump up a block. Maybe this is a linked problem. I will do some tests with other mobs.

Seams to be a problem with all friendly mobs. I have attached images. In the images they just jump up and down when trying to follow up blocks. When stuck they just jump up and down. This is shown in photos two and three.

The last photo is the set up i am using for the second problem.

Zombies do not encounter the same problem when following villagers or the player up blocks. But i did discover a bug with the baby zombies riding chickens. Photo is attached.

Another bug found in testing this one bug! Lighting glitch! Photo attached! It is on a chunk border. When blocks were interacted with, E.G. me falling and landing on it, the problem was sorted. Couldn't recreate glitch.