When the aeldari are performing their "seventh path" research, the tooltip says that " if the aeldari perform -1,1,2,3,4 steps, they will sweep the galaxy!". I can't understand how many times I can fail to stop the aeldari. Also: what does it mean that they will sweep the galaxy? Will the campaign fail automatically or will the aeldari keep launching an invasion every single turn? Or will they literally invade every single system at the same time? Does the aeldari side quest stop this thing too?

I also think that a two turns timer is too short. I'm on the other side of the galaxy and can't reach that place in two turns. You might say "Well, that's your fault, because you have to be present in every single sector", but how am I supposed to be present in every sector? I can't possibly hold all my territory, I have to defend against invasions. I only have 3-4 fleets to spare and they can't be everywhere at the same time.

I think it causes an invasion in every sector each turn until the system is captured. I didn't let it go off in the Chaos campaign I just finished, but I also lucked out and the effect triggered right next to my front lines (so that system was next on my list to attack anyway).

Eliminating the Eldar faction should also (theoretically) stop this effect, since it reduces their threat in all sectors to 0, and invasions require threat.