I don't know how to fix the issue; I think it's related to the new spy system and/or city capture popup. Waiting on G for that.
My own Civ V modding skills are basically nil but poking around in error logs I found this:
[265734.437] Runtime Error: D:\Documents\My Games\Sid Meier's Civilization 5\MODS\(6c) 43 Civs CP\No-EUI\NotificationPanel.lua:245: table index is nil
[265734.437] Runtime Error: Error loading D:\Documents\My Games\Sid Meier's Civilization 5\MODS\(6c) 43 Civs CP\No-EUI\NotificationPanel.lua.
I'm guessing that's the source of the issue; as you expected line 245 is:[265734.437] Runtime Error: Error loading D:\Documents\My Games\Sid Meier's Civilization 5\MODS\(6c) 43 Civs CP\No-EUI\NotificationPanel.lua.
g_NameTable[ NotificationTypes.NOTIFICATION_CITY_CHOOSE_FATE ] = "ChooseCityFate";
Going to go ahead and see if there's anything I can do to patch this.