Glow Squids can still spawn in bodies of water in the Deep Dark, even though the Deep Dark should be free of mobs spawning.

How to replicate:

-Find a Deep Dark

-create a pool of water

-stand about 24 blocks away

-wait for a bit

Expectation:

Glow Squids never spawn, as mobs of any kind cannot spawn in the Deep Dark

Reality:

Glow Squids still spawn somehow