City state can’t be captured and isn’t listed as occupied by any of the AI Civs.

[Joe Marzen]

I’ve been trying to capture a city state with various melee units... As many times as I attack the city I never get to actually capture it. Yes, the defense stats have been reduced to zero.

One slightly odd circumstance. The city is completely surrounded by an AI Civ except for one hex, which I occupy.

The city also isn’t listed on any of the AI Civ’s city lists. It also isn’t listed as a option for trade or as a potential location to send whatshername that Governor.