I've tried playing M5 Forge co-op twice now (with another player) and both times the map fails to expand/progress after destroying the 3rd strategic missile launcher.
I also tried it playing solo (through FAF) and didn't have the same issue (after a minute or two it progressed).
My replay.log didn't update for either game but I've attached the game log from after exiting out of each of the games where the issue occurred, and the fafreplay file from the 2nd attempt.