Hi. My friend found that not all tracks are visible to him all the time. Firstly, he does not have any track DLC's. (I know, right ) Initially we found that he can see tracks he doesn't own in MP. I googled and aparently that's normal which I think is a really cool thing for Reiza to have done. I have had no problems seeing the entire list of DLC tracks. I have bought all of them. In his case, he sees all of the tracks at the point of lobby creation but once in lobby some are no longer visible to him. Some are, some aren't. Could this be because he doesn't own all (or any) thracks?
If you set a high number of player slots, e.g. 32, there are some tracks that don't have enough pit stalls for that many cars. These tracks will not show up if the lobby is set to a higher number than the track allows. If you create a lobby with a lower number of player slots, e.g. 24, almost all tracks will be available to choose in multiplayer.