The game becomes soft locked when a given city cannot construct anything due to being encompassed by the siege of another city, which prevents it from building districts or units. 

To reproduce this, simply create a second city next to your first, and get sieged by a sufficiently large army such that the battlefield includes both of your cities entirely. 

Attached are save files for the moment the game is stuck, as well as the start of that turn and the preceding turn. 

Turn stuck.ctr

auto-save 18597.ctr

auto-save 18596.ctr