Pokémon from the underground spawn pool are spawning in Jungle biomes.
Upon investigation, Geodude, Gastly, Zubat, Rattata, and Diglett were all listed as /checkspawn common spawns with a higher weight than any Jungle Pokémon (aside from Bellsprout).
These Pokémon far outweigh normal Jungle Pokémon in spawns, therefore causing a pretty major issue.
This issue was not found in any other biome; cause unknown.