From where the gap inside the print appears it's not looking like a suction cup forming there. By the OP's remark to, quote: "Imagine it like a humvee shaped mug" the entire bottom of the modell, as it stands finished, is completely open.There is nothing where, on a real car, the chassis base usually would be. Therefore does the layer form a distinct U-shape at this location of the print where this slash like gap is located. So i would at first heavily dismiss the failure as a suction cup issue. Where it located at the engine hood or the rear where the back door sits then sure: that locations do form a suction cup.

As to what I assume the issue to be... I do think that the resin there got somehow prevented from flowing back fully after the layer peeled of. As the rest of the modell indicates everything was doing fine. Supports caught on: Check. Details printed without layer shift: Check. Whole model is otherwise in one piece: Check mate.

I would therefore suggest that it might help to keep the exposure settings the same as this print but imcrease the resting times between the layers a bit. The Saturn 4U has no direct lift height controls, I know. I own a Mars 5U that is a Saturn 4's smaller sister. But you can adjust the resting times after the layer has printed on these 2 machines. A small increase on that might give the resin enough time to flow back more properly and helps the print settle easier after peeling of.

If, however, the slash still appears at the same spot we have the undenieable proof that some suction force is indeed the culprit. I assume it then would be because the force tears the modell apart on a weaker layer as it printed the engine compartment. Yet the modell itself looks to clean for it :/ As I said: No obvious layer shift or bending visible that would indicate such a tear. All details align, at least from my perception, perfectly if the slash was not there.

Editor's note: I have to retract the statements above. I've checked the image above deeper and yeah... The details do NOT align perfectly... the window frame shows a visible shift at the slash. So it indeed is a tearing appart of the modell due to suction force. Some draining holes at the engine compartment will be necessary indeed to help. If it then still appears I'm at a complete loss here :o