[Q]

To revive this older topic: Now I had the same problem with carriers loaded full of fighters and yet in combat they didn't launch them. In tactical combat you couldn't launch the fighters either.
The cause?
It seems that if your empires has reached the maximum number of units in space this will prevent the fighter launch! If I scrapped units below the maximum number all returned to normal.
IMO this is a bug not a feature. It is not reasonable that carriers cannot launch their fighters in a combat no matter the number of units already in space.