Hi there!

Do you happen to have your save where you ran into this still? If so, could we get that from you? Your saves should be located here:

PC: \Users\[username]\Documents\Humankind\Save Files

Thank you!

I faced the same issue with Uranium - actually I already had 2 sources in the same city, so I thought it is a bug that UI still offer to build a mine after it already been build. After reading this topic I checked my game and found invisible source in a water (on south-east edge of the Cahokia)

Invisible_uranium.ctr

Yes I do have a save prior to when I built the well,  you can see the oil in the water and it's sparkling a bit now that I look at it , but no marker.

I looked to see if I had one prior to when oil becomes visible to see what the hex looked like then,  but I did not.

Here ya go,   hope it helps.    It's on the bottom of the map,  small outpost, wistred I think is the name.

Siege Test.ctr