Abyss monsters outside of terrain

In "penitentiary" map an abyss pit spawned close to the edge of the map, and a rare monster spawned/got moved somehow outside of the map edge, behind a fence.

I can see the monster hp bar and it isn't full hp, but can't hit it with any abilities so the abyss is impossible to complete.

The monster has shroud walker mod, but isn't able to teleport to me at all either.

It has a minion "swarming wasp", not sure if the rare is the same monster or if that has any effect on this bug.