May be you are already aware of this problem, good people of EB team or may be not. Anyway, when playing for Aedui I lost one city with level 1 government to Romans.

Retook it couple of turns later. Destroyed their newly built Roman government and repaired my Level 1 government.

Then I saw "pacifying newly conquered region" building option or whatever it's called. So I built it and then I could see that it's possible to build Level 1 government again, despite that it's already built. So I ended up having two Level 1 governments in one city which sounds like a bug to me.

There you have it.

Cheers