I recently went to a lush cave in my world and spent nearly an hour witing for axolotls to spawn to no avail, i then spent about 2 hours building a closed off water filled box to try to spawn them also to no avail.

to replicate using my seed, use seed 1029446582854060852 go to x-1250 z-1260 and mine into the lush cave. even making the entire area dark will not spawn the axolotls