Disappearing Wonders?

In one of my cities saw Petra was available and kind of mentally earmarked Petra to build next after my monument. When the monument finished, Petra was no longer in the list of things available to build.

Here's the strange part. I could see a lot of the map by then and quickly explored the rest (to take revenge on whoever stole it from under me) but it was nowhere to be seen. I looked around the entire map several times and Petra hadn't been built anywhere. I also 100% still had valid tiles to place it on, so that's not the reason it disappeared.

What could have happened here? Is there a bug with this sort of thing, or is there some mechanic I'm unaware of? As I understand it, the distant lands civs don't actually exist until exploration but does the game "dibs" them wonders at random points or something like that so that they can generate with antiquity wonders? I've never paid attention to if any distant lands cities have any antiquity wonders in them. Anyone got any ideas as to where Petra went?