They keep casting through walls. I recommend you to just delete the blightstormers’ ability to cast anything at all, like “fixing” the map skipping carriers’ ultimates by nerfing them, not actually fix the exploits themselves in the 2.1 beta - nice job guys! 
This is one of the many spots (where the crosshair is) where they can cast through wall.
And another, on this you can see the green remnants of the cast.
Of course these blightstormers cannot be killed, because they are out of players’ reach until they teleport to playable parts of the map.
Have a good holiday