When having their spawn rate increased across the board (weight=50, mingroup/maxgroup=3), hellhounds still don't spawn in Nether Wastes and Crimson Forest biomes. This feels like a bug due to me scouring the nether in creative and not finding a single hellhound. Even with their spawn rate cranked up so high, I've yet to actually find one.

Update: Can't find any in the warped forest biome either.

Do you have any nether mods installed? BetterNether and BYG don't set biome categories so they become extremely rare

Correct, BetterNether is installed, would you guys be able to make them spawn in BN biomes?

Otherwise i'll open an issue on BN github.

No, we rely on biome categories (a vanilla field) and if a biome doesn't add that, we can't do anything about it.