Not an expert, but it is probably Project 6T. In the game files that I've seen, the eras are depicted as numbers. (Ancient Era is Age 0, Classical is Age 1, etc.). Since Project 6T adds additional eras, that probably shifts whatever number the world congress has in this mod so it's in an earlier slot.

Confirmed it starts on the Renaissance without the other mod, not sure what could be causing this... I do use Project 6T, could that be it? Might I ask for compatibility, if that's the case? <3

Heya, I love the mod and the cooks over Better World Congress, but I'm having an issue where the World Congress is starting on Renaissance... I looked into my mod list to see what could be causing it and I didn't have anything suspicious, although I did have the "World Congress Start at Industrial Age" mod, which I forgot to remove...

But could it be it? I mean, your mod makes it start on Industrial already, and then another mod tries to do the same, could these two mods trying to do the same make it start on another period altogether? lol