Broken unit id is easy: remove all units from map LOLCould. If an id reference anywhere is flawed nothing will fix it but for some variables, recalculate may help. And yes, at that stage of the game saving every round may give you a fighting chance to extend things out as far as you can.
All units that exists are animals, police force, workers and great people in my game.
So I'll just cleanese Earth sector from all units.
Can city ID reference break too? If yes then I'll gues I'll remove city X if clicking on city X crashes game.
So it seems like fighting severe radiation poisoning or cancer.