Killtech
Discutator
I deleted Castles because of that bug discussed above.
But it seems like it isn't Castles fault or maybe not entirely because I still get this:
guess the amount of buildings that use BombardDefense must be reduced to a very small amout. alternativly one could add there a cut off value such that always at least 1% damage is done - no matter what siege weapon attacks. hmm... this cut off could be made dependant on the actualDefense/maximalDefese and bombardDamage-BombardDefense in such way that the cut-off only is applied until a certain minimal city defense is reached. after that the siege weapon must exceed the bombard defense.
nice amount of gold in your screenshot btw.