There are many existing bugs in this game, but one of the most annoying from my perspective is the following online lobby -related:
I've met this bug basically every day I've been playing GT6 lately (in international lobbies where players are mainly from Europe).
When you join a lobby, you can see other players on track during the first race as supposed. Then after a couple of races your fellow racers start becoming invisible. If you rejoin the lobby, you can probably see everybody again on track...unless the lobby is compleately broken in which case you have to create a new lobby to fix the problem.
From online player's point of view these aforementioned bugs are really disturbing. These bugs have existed for a long time (and I rate them very serious) so PD should have had time to fix them. So don't they care or are they just incompetent of fixing them?
(BTW: I don't know how the FIA Online Series will be implemented, but these online bugs could be some kind of a "showstopper" to that effort also...)