Could you share a game log? You can find them via the client:

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It sounds as if you previously had the Sorian-updated 16 player lobby mod. This was often distributed as part of the Sorian AI, but it was also distributed as a standalone module as well.

Did you start the game from your steam library or from somewhere else (Desktop shortcut, FAF, etc.) ?

If you started it from Steam you are probably looking for a non-FAF mod that mods the Vanilla steam lobby to support 16 players. Can you remember where you found that "updated lobby"?
Or maybe you added the FAF version (non-steam) to your steam library as link, in which case you would have to install FAF first.