I noticed in several games that there are no discoveries in the water (ancient/medieval era).

But while moving a boat in search of them I got a "Curiosity Collected" notification (there was no fog obscuring my vision).

Turns out the discoveries existed but were hidden.

I cannot provide a save file since reloading the game will fix the problem. (many discoveries become visible in the water)

I played Bantu in ancient era (which creates food curiosities), but it might not be related.