I recently arrived on the second island, did the whole poker thing with Sam and then went off to climb the radio tower in the area. After I did this I started the supply drop mission that just became available. But I failed, and when I hit retry I ended up standing pretty much where I was when I failed the drop. Now that supply drop mission is gone and everytime I climb a radio tower and it tells me that a new supply drop mission is available, they're not there.
Anyone know what the hell is going on? The vehicles are there, but no missions. I tried rebooting the system, I tried continuing the story (just finished the Doppelganger mission), and nothing.