It happened once to me Last month, when I started the game as usual, suddenly the mastery rewards cars appeared with a cost of 200 to 300 credits. I also found out that every token cars were converted to credits. I bought the first two mastery cars - Camaro Z/28 and Datsun 280Z at that time. But when I finished a test drive with the Camaro, everything was back to its usual cost. I think it could be a server problem.