Immortal Corpus Crewship appear in Grineer Skirmish Railjack mission

[YizTJ1259]

I choose the Void Storm (Axi Fissure) - Skirmish (Grineer) mission on Nsu Grid (Veil Proxima). After loading into the map, I realize that there're no any Grineer Crewship, only several Corpus Crewships.

And I can't destroy those Corpus Crewships, neither by using Forward Artillery or sabotage them from inside. As you can see from this image, their reactor is destroyed, but the Crewship is still functional.