[2021] Waiting for player to catch up

Is this just in one particular campaign? Or also in a new one you might start as a test?

Whether you are using Steam or Nakama MP option at launch, try the other one - any different?  

dockens said: We were using steam, I guess? Doing multiplayer through the in-game menu, but we are both using Steam installed versions of the game.

When you run the same from Steam you get a small dialog where you choose MP type. Two of the options are Steam and Nakama. If you chose Steam before, as it sounds like, please both choose Nakama instead - any different?