Nuclear_harvester, thanks for your reply !
The fact is in my case, I modified some .ini files to increase the max amount of spice the harvesters can get in one go. I did it to make the game more difficult, as I noticed it made the enemy AI produce much more units (so much that their are quickly overloaded !).
Apart from the survival mod, I encountered this problem in an map where I played as the Emperor. And as far as I remember, there were no aerial reinforcements in this map. So I wondered if the delivery crash was caused by the spaceport, or by any new united produced ?
Sorry if I tend to repeat myself...