I twice encountered these similar bugs:
In "Fort Clarke Assault" killing the red Cybran Commander before getting the last mission to destroy the 3 defending enemy commanders will result in you beeing unable to finish the mission.
Killing the the T4 Seraphim bombers prematurely with Artillery in "Red Flag" prevents you from finishing the mission. Tho, you still receive the scripted messenges for completion time of the bombers - even tho there are none.
Did you mean destroying the Seraphim T4 bombers in Red Flag instead? During our speedrun attempts about half of the attempts on Red Flag were bugged and we weren't able to complete the mission. We weren't able to figure out what actually caused it since we basically did the same thing every run.
I found a generic bug regarding all coop missions where the setting "Timed Expansion" on or off still triggers after 25/20/15 depending on difficulty easy/normal/hard.
@Fringillus this likely means something crashed, halting the executing of the script that is supposed to help you move on with the mission. Best to share the game log in this case so that we can see what is going on. Same for @archsimkat
A work of art is never finished, merely abandoned
I'm having issues playing Aeon mission Shining Star in co-op. When launching the map in a team with Common Army enabled, the map loads but never starts any script so all we see is a mostly unexplored map, with no voice over or mission objectives appearing, no ACU warps and no units to control. Seems to be frozen. In our testing it seems to work when we disable Common Army, I can reproduce this even with a bot team-mate instead of a human. Logfile from that game here.
We've been playing the previous Aeon missions without any problem, and the first 2 of the UEF ones - no issues with those when Common Army is enabled.