When selected, Temple of Essence for Empire faction can't be build on normal tiles, exempt on those already marked as city tiles.

It's a simple error in XML file. Temple, unlike any other building, is missing Land as SupportedTerrainType. But has City. So only if tile is already converted to "city" (by building any other object on that tile) it can be built.


P.S.
Exempt this bug, there is also balance issue of +50% essence bonus stacking with itself. Built in two cities that is +100% bonus to mana, ten cities +500%, twenty: +1000%. It's a bit too much.