Monsters Not Properly Unloading After Unstable Breach Ends

Bug Report ID: #925,327,976

This has happened in two map instances today after not experiencing it prior (scarabs, map types, etc. have not changed recently).

When an unstable breach ends, there are some maps where enemies will not be unloaded. Their model becomes invisible and they cannot be damaged. They still exist in the map because their name will appear on cursor hover. Their AI is still loaded as well because they can attack and effects like Delirium and rare monster modifiers (e.g. lightning storm) will also launch attacks at the player.