Breach monsters spawning inside terrain

Stabilized a breach and one of the rares that spawned came up inside map terrain. This made the monster unkillable and by extension meant that I could not complete the breach and/or get any rewards for it.

Not a common occurrence but if it happened to me, I suspect it has happened to others.

Video clip of the mob in question: https://youtu.be/4EuUEte01SA