Object diffent altitude

Hello, a question.
I created a long .mdl object like a landing strip.
I place it on ADE and then save the scenary (I did a flatten on the whole airport), but the object on one side is aligned and leaning with the ground and on the other side raised from the ground for several centimeters ... what could I do wrong?
The ground polys are also raised from the ground at the ends of the airport, while in the center they are anchored to the ground.
Sim P3dv4

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