In various frozen biomes, the only hostile mobs that spawn are the skeletons (as expected most of them spawn as strays).

Steps to reproduce:

1. Create and open a new world with seed 297169206, mob spawning disabled, and always day selected.
2. Issue the command /time set midnight.
3. Issue the command /tp 626 86 -285.
4. Issue the command /gamerule domobspawning true.
5. Wait until a bunch of mobs have spawned.
6. Issue the command /kill @e[family=monster]. Note that only strays were present to be killed.

Additional information:

• The pinned comment contains root cause analysis. In short, the biome JSON files are missing the "monster" tag.

Affected biomes:

• Frozen River (frozen_river)
• Legacy Frozen Ocean (legacy_frozen_ocean) - no longer generate in new worlds
• Snowy Mountains (ice_mountains) - no longer generate in new worlds
• Snowy Plains (ice_plains)

This report (including comments) uses a mixture of Bedrock and Java biome names. The following table can be used to translate the Java names to Bedrock biome names.