Theres the log and my username is "White935"
I only have a single city. Orc (swamp) called "Skraag" (city of orcs).
How to replicate: (it is consistent, and occures without fail)
Enter World map: Controle One of the armies. (i use the one with the hero).
Go into PVE (appears to happend with pvp too) (zoom button) and i fight and loot a bit, training my troops y'know. in the rolling plains at the moment.
then i end the combat, returning to the world map. then return to the village view and the great hut will have ceased to function.
About your theory about turning into a gaia building (natural world building) is what i suspected aswell. due to the colors of the letters and behaviour of it.
Other bugs which is noticeable from it:
Palsiades being rebuilt inside palsiades gates whenever you log in.
Also You can see that your unable to build mounted units ( the unit just disappears once it enters the warg den, but dosnt begin construction of said mounted subtype). aka they seem to lose their way inside the building <.<
Local issue: Orcs labourers insist on not mining stone no matter what, and must be restasked whenever you log in.
Edit: By the way Could you Devs confirm that am unable to build "Stone Walls" or aka The Next upgrade after palisades. the button just disappeared from my great hut after i bought the Upgrade From the temple.
And now the upgrade citadel buttons back.. seems like it has lunch hours i didnt know about