Any idea?

Does anyone know what this could be? One day this floor was clean and the next there was this pool present that is impenetrable/solid and unable to be scraped/chipped. We can’t tell if it has come up from the floor or out from the wall. There is nothing present on the other side of the wall so it’s just here…. We are on the first floor of a three level condo and our building manager has said that after checking with the two units above us nothing is out of the ordinary. I’m totally stumped…