When the server use a specific starting gamemode (races - in this case), In some scenarios, a lobby split can occurs for recently joined players.

IV-Racing-Club server use "Races" as main gamemode. Server seems to work fine when a low number of players join, everyone joins directly to the same and only lobby. But, when the number start to increase, a lobby split is more possible. (At least in GTA IV).

For some reason, in TLAD DLC the issue showed in a persistent way. We did a event on the previously called server, and, every joined player were sended to a different lobby. They had to manually go to freemode, phone, multiplayer > player match > lan > quick match > race, to join to our principal session.