First fail I had a smaller throne room filled with a table and chairs, still valid as the quest wouldn't let me accept it until the throne room ticked the check boxes. My bedroom didn't have floor. Bestower went to my barracks (not bedroom) and it failed with message that bedroom was no good. Vanilla no mods.
Second fail same crowded throne room, fully acceptable bedroom, bestower went to stable and failed. Vanilla no mods.
Then I built the larger throne room seen in picture. Bestower went to stable and failed. Added mods by this point.
Awesome. Let me draw tester /u/pheanox 's attention. We will investigate!