Ok, so this is not a bug? It's just that there is a % chance on if you get additional tiles, and how many (max of 2)?  That's kind of rough for something that you have to find, its a limited supply and so you try to use it very strategically.  Really wish they made it a little more consistent. 

It seems like perhaps the artifact isn't able to tell which tiles are already available on a planet.  It would be good if it was able to check to see if a given tile is already buildable and if so, re-select a tile until it gets a free tile.  Or if a tile is already buildable, give the tile a 3x buff for all disctrict types if it doesn't already have one.