This bug is likely due to some art not being finished for a few tiles. The tile says K_SkathPit_01, which is a tile that does not exist. There are actually 3 buildings that are using this tile name. It would seem to be a placeholder for art that will be added later. It would have been nice if they picked a placeholder tile that does exist, but you can always just use a tile you like that is already in the game. I made my own tiles for each one from the WoM tile designer and added them to the new game. I wonder what the dev's version of Onyx Throne will look like.

It was the best L5 building for me, so I picked it and could not build it.

Anyone have a full list of the special building options at L5? Maybe a full list for each level?

One L4 city with a prison and one L5 city with Onyx Throne and  normal tax = zero unrest

I always get the same upgrades for each city as population means more then anything else for me.

L2 = Garden

L3 = Bakery

L4 = One city with prison, the rest the research building 

L5 = Onyx Throne (but I normally only get one city to L5)