Looks like I reproduced it with a new game, this time its luckily one that I had saved from last night and its not that far behind.

compare the last time I CTDed: https://forums.galciv2.com/?ForumID=274&AID=121630#942669

now compare the last several lines of this debug err from my game:
Debug Message: Random Event: Begin
Debug Message: Random Event: End
Debug Message: BuildShip: Cannot build ship type 6-Frigate M11-3 at Haber III - No open slots
Debug Message: Destroying ship Korx Cruiser M8-1 2144. Orbiting: 1
Debug Message: Was Orbiting: Haber III
Debug Message: Destroying ship Korx Cruiser M7-8 2154. Orbiting: 1
Debug Message: Was Orbiting: Thuban I
Debug Message: Destroying ship Korx Constructor M9-7 2836. Orbiting: 0
Debug Message: Random Event: Begin
Debug Message: Random Event: End
Debug Message: Destroying ship Terran Constructor M9-7 2803. Orbiting: 0
Debug Message: Destroying ship Korx Constructor M9-7 2831. Orbiting: 0
Debug Message: Random Event: Begin
Debug Message: Ship does not have a valid ship class in CalcTotalMoves. Setting moves to 0.
Debug Message: Destroying ship . Orbiting: 0
Debug Message: Random Event: End

the last few lines are exactly the same or almost the same as the last time I CTDed, so there is something common here.

since my game hadn't progressed very far from my save, I'll see if it happens again.