Sorry for the delay in responding, and thanks for the suggestion, but I already had that option selected. I've tried deselecting it too, and that doesn't solve anything either...
The track in question is Fuji Speedway 1968 by William TRiker updated by Rainmaker, version 2.0. In some places it's visible correctly...
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... but in others it looks as if the asphalt is melting in the scorching Japanese summer sun...
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By the way: my dear friends, don't even think about stopping in the middle of the track to take photos; they look great on Instagram, but you can cause terrible accidents...
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And yes, I know, the car isn't from that era, but it's one of my test cars, and that's the magic of Assetto Corsa: you can make almost any combination, no matter how crazy it seems...