Margins
Tesla pays their suppliers after they've sold the vehicle, so when deliveries go up every quarter that works very much to their advantage. They get a bunch of raw materials delivered, turn them into a car, sell it and get cash relatively immediately, and some weeks later pay the suppliers for the materials.
When deliveries are ramping up, you're always selling more than you're paying for, in effect (production vs deliveries). But when deliveries decrease, now the opposite is true and you have to pay for last quarter's production (305K vehicles) while delivering fewer (255K) in the current quarter.
That's going to deplete the cash stockpile, so to partially compensate, you take longer to pay your suppliers.
In Q3, we'll see the pendulum swing the other way, as they'll be paying for the Q2 production while delivering far more vehicles. Total payables may increase next quarter despite what they do with the DPO simply because they brought in far more raw material to produce more cars. But on Sept 30, they're going to have sold another, say, 400K vehicles, while essentially paying only for the 258K produced in Q2.
Then in Q4, they'll hopefully sell, say 440K vehicles, and be paying for the 400K produced in Q3. If sales were flat every quarter, it wouldn't matter as much.
I think they've managed this aspect very well in Q2, though being a Tesla supplier sounds like a rough gig.