Some sifter enemies randomly stop moving or become passive if too many spawn at once

During a fight with a Soul Corrupted Harmonizer, I was in a situation where it spawned too many sifters at once, in which some of the mobs started freezing in place (in poses similar to key art, coincidentally) and not attacking until I got close.

Expected: Mobs should continue animations as per script, regardless of the amount of mobs already around them.

Observed: Mobs have either randomly gone passive and ignore the player or freeze entirely.

Steps to replicate:

1. Start a (Soul Corrupted)/Harmonizer mini-boss fight.

2. Run in circles until there is a large amount of living sifters.

3. Some (commonly Seedlings and Nesters) sifters will stop attacking the player and wander passively or freeze in place in key art poses until re-confronted at close range.

The video was taken in the aftermath of the Harmonizer fight