Exactly what it sounds like. I've had this happen twice now, I load into the mission (both times as UEF), and do the normal stuff, but when I have the area cleared so Fletcher can port in, he gets there but the map doesn't expand. No dialogue plays for Fletcher getting there, or for anything else. I even accidentally killed Fletcher with an artillery barrage and that dialogue didn't play either. This only seems to happen on Mind Games, as I've played Black Day and Overlord with neither one having issues like this.
Mind Games (FA Mission 5) fails to progress past 1st stage
@the_blyatman There are reports of that with some missions. I'd suggest that you head over to the FAF Campaign Development Discord, then check the getting-started channel & the public-uploads channel to see if there's a more recent version of the mission you're playing. If there's not, then you can make a post in their bug-reporting channel.