We have had it numerous times in our league races, on one occasion 9 cars got stuck while the room host chugged around with someone else for the remainder of the race.
We have had to set our lobbies up without the compulsory tire change option, that seemed to be the issue, along with the mandatory pit stop option. Both options are very glitchy, add to that the fact that you can't actually check what tire drivers are on as the replay doesn't show the change.
Yet another PD screw up .... *sigh*