I have spotted a difference between my correctly displaying campaigns and the campaigns that spawn duplicates ... sorry if this is a red herring. When I look at the Details tab of the correct campaigns in Firefox in MacOS, I am the last person on the player list (aka farthest to the right) since I am GM and created the campaign. This is how the players list has been ordered since I joined ... the GM is last on the list and new players are added just to the left of the GM's picture. Still talking about Firefox here. For the "bad" campaigns that spawn duplicates, I am not the last person on the list even though I created the campaign and I am the GM. On one campaign, I am farthest to the left out of four players (opposite side of where I would expect the GM to be). In another, I am second to the left out of three players. On the last one, I am the only player. Let me know if this makes a difference. Cheers!