i've noticed something in Mission General Mobilization, while sending quests to my friends, and is that if you lag you actually deliver 2 quests in a row if you click twice on it (the quest you wanted and the following one in the list) to the same person without actually needing to select the name.

I'm of the idea that something similar happens in plunder screen.

When you select an SS convoy, if you lag, could be the SS convoy is no more there server side and so its spot gets taken by the following mission that was in the list, that could be also an S or A mission, so, when you click on 'attack' you think you are clicking on the SS one, but the SS one is no more there and it's replaced by the following (or new) S one that's the mission you are actually clicking server side.