Error adding a new POI

I have a particular private world I have trouble adding new POI. I can add new areas, characters, etc. I just have trouble adding POI. When I click on “Add POI“ and place the marker in the map, I get the message from the screenshot:

But, I am unable to find anything that could resemble a lost “New POI“, hidden around in the map that could be creating this problem. Getting into a game in this world and asking Franz to generate a new POI works just fine. Cloning the world didn’t work, as the problem got copied too. I’d be glad to get some help and thanks in advance!