I think that imposter cosmonaut guy has something to do with it. I didn't kill the cosmonaut and got tunnel 6 to breach. When I did kill him it seemed harder to get it for me.
Although someone said kill him and then when he respawned it breached so it's probably just random. It was a pain at times getting that tunnel 6. You are going to just have to deal with it. Unless someone knows for sure but never heard of anything else. Besides just let them breach until you get tunnel 6 but I don't like that idea. I always hacked them before.