I saw a post on Blizzards forum where player was saying the Uber Ancients jewel was only dropping like 50% of the time. I thought the jewel, like a torch, was 100% guaranteed drop. The RNG was on which Ancient you killed last, and that would be 1 of 2 types. I do remember seeing something about if you were at the edge of the plateau the jewel could drop out of the map essentially.

For me the drops are 100%. Do I just have luck, or is this person an idiot?

You probably just misunderstood him or he worded it badly. Drop is 100% chance, but there's a 50% chance to get the specific jewel you want.

There used to be a bug, where the jewel didn't drop at all, but it was (supposedly) fixed, according to Blizzard.
There's a high chance that's why that person came to that conclusion.

I reread the thread, and they are adamantly claiming it only drops 50% of the time. I got worried for moment as I am gearing up to do a run in a few days. I think they might just be a moron.

i read from somewhere if you are at edge the jewel drops outside of map.