Unkillable Breach Monsters

In a Breach Hive while delirious, breach monsters sometimes reach a state where they are unable to die. They consume pierces, extra strikes, and still receive on-hit effects with zeroed out HP bars but do not disappear. Ailith's abilities do not kill them, however they can still be stunned and frozen.

They can damage Ailith and cause the encounter to fail.

Update with an image in case it helps - I do not have southbound equipped.

https://gyazo.com/73485be52fb3fd538ffba191c54ed28d