And just another little glitch in the game.
For the achievement “Flooded” the requirement is “Complete all co-op missions”.
However, I just unlocked it without ever finishing the 5th (and last) co-op mission.
This is how it happened:
I played (and finished) the first four co-op missions during the course of the last three days, with different co-op partners.
Today I found a random online partner for the fifth mission. We played the mission, but both died, therefor not finishing the last mission, we were not even close to finishing it (we died after the destruction of the very first energy core).
However, my co-op partner decided to play the very first co-op mission directly after that, which we finished successfully.
As soon as we had successfully completed the first mission, “The Company of Strangers” unlocked for me, as well as “Flooded”.
“Flooded”, as I mentioned before, should not have been unlocked at that point, as I never had finished the last co-op mission.