In every world I create I end up making some sort of spot for axolotls (an aquarium, pond/pond with an underwater cave) and every time they swim to the ceiling (unless it's a pond with no underwater cave) and stay there, sometimes they swim under a block and stop there. I thought it was the kelp but when I broke it they turned to leave the spot but froze in place again. I made sure that all water were source blocks.