I don't know what happened tonight, but during the Fleet Mark Event, I have done 4 space missions and in all of them, we finished with only 4 peoples. Than I tried an STF elite, than again, only 4. I don't know if it was a bug or just a bunch of peoples that decide that they didn't want to do it after all. but it was very annoying. In at least one, there was no reason for the fifth person to quit, the mission was going well, we even manage 16/27 transports, which is good even with 5 peoples.
So please, if you don't really want to do it, don't. It's annoying to do the 5 persons missions with only 4, because one live just after the beginning. If it was a server bug, please fix it. I admit that I myself quit the STF when I saw that once more, we loose a player at the beginning of the mission. It happened to me a few times, peoples have a computer crash, sometime people quick a group after a while because they have done a lot of mistake. But 5 times in a row, at the beginning of the mission. That's not normal.