Blight bosses/unique mobs spawning in between map terrain are immune to all damage

Hello,

I just ran a city square map and the blight portal spawned between the map shields/obstacle. I could kill the small mobs but the unique mobs and boss are stuck, and no damage can be done to them. It is not the first time this happens.
Bug id from using /bug is 2372397034

https://imgur.com/a/CjorRyW