I've noticed that. First time I saw it I was like "WTF?"
But that happens in like all online endurace races that you save so whatever .
(Annoying when I want to see how other people's tire wear looks)
I've seen what you are describing at least ten times while watching replay's of the other AI after an Endurance race. I think that I first saw this around a year ago, so I can't really pin-point which tire version caused this to first occur.
It does not always occur during replays, but when it does, it always seemed to occur just after a pit stop.
Its like the game can't quite decide how to show the wear for the new tires.
It eventually seems to settle down. I usually switch the replay to another AI and then come back to the first AI and the tires will usually regain their appropriate appearance.