Mobs spawning in excessive quantities and ignoring the game's creature limit, spawning is also abnormal in which mobs only spawn in groups of 4-8, and both hostile and aquatic mobs try to fill their caps instantly, treating it as a minimum rather than a maximum.

Test Video:
https://youtu.be/Pba-vZNLpe4
Seed: -6973248283818474784
Coords 1: -1626.433 / 66.00000 / 732.763
Coords 2: -3410.374 / 69.00000 / -2492.913