I've got the supplies needed for several relief missions but when I go back the the sector I got them from the from the "Continue Mission" button appears for a brief second after loading but then immediately disappears.

Can't help ya on that one other than to say to skip the Aid the Planet missions. Not worth the time involved when you can simply leave the system and pick a new unexplored system.

Maybe so, but its still a bug that needs to be fixed. I save them up, collect 3 or so, get the stuff before I log out and turn them in the next day, that's a few hundred skill points right there. And I've found that if I skip them I'll get Aid Planet back to back to back until I do accept them. Some ppl do like to help people and not always just pewpew them to death.