The axolotl get stuck while try to pass a wall underwater. Even when I try to push to release them, the axolotl continue stuck. Only when i break the wall they move freely. So it seems the their path through the wall is locked somehow, maybe because it is not a full block and, since they can "enter" to that block but cannot pass through it, they will try indefinitely to pass it. Axolotl: "I will pass through this block no matter what, even if I use all my spawning life trying it"
In the image you can see 4 axolotls stuck.