I had this same issue, I solved it by duplicating the affected civs and deleting the old versions.
Thank you for your reply.
One of the Civs listed in an error was a faction Called something-something-Tellar. I can't find that Civ anywhere on Steam or Nexus. I would gladly install it if for no other reason than to get rid of the error messages. I would do the same for all the others, too. There must be about 10 of them.
The game works fine, otherwise. I've never had a bug in GC3 before now. Never.
Again, thanks for the help,