Pre-existing worlds from before 1.18 do not properly update biomes in underground sections.

Worlds that existed prior to 1.18, and likely 1.19 with new biomes aren't recognizing what the biomes are underground, in regards to local mobs/fauna and the temperature for that biome. For example I found an ancient city in my world I have had from 1.16, and above it on the surface is a desert, and a river/small ocean biome. According to what I have read, the temperature of the Deep Dark biome is supposed to be 0.8, thus allowing snow golems to be made and to survive in that biome, disregarding hostile mobs in this case. When I create a snow golem in the ancient city I found, in certain areas it'll start dying as if it is in too hot of a biome, but in other parts of the Ancient City, like under the surface level water biomes, it doesn't take temperature damage. I have also found multiple Lush Cave biomes and have yet to find a single axolotl in them in that pre-existing world. The snow golem temperature issue doesn't exist in a newly created world either. It could be something to do with that issue that is also causing the no-hostile mobs spawn rule for Deep Dark biomes to not function on Bedrock.Thank you and I hope I worded this clearly enough to be helpful.