For landscapes, both the simple and complex collision are used when simulated against.
Open the advanced vehicle template project.
Set the landscapes Simple Collision Mip Level to 5 (Verify that Player Collision and Visibility Collision views are different.)
Add a sphere to the level above the landscape with simulation enabled
Result: The sphere will collide with both the simple and complex collision.
Expected: The sphere would collide with just the simple collision.
There's no existing public thread on this issue, so head over to AnswerHub just mention UE-65736 in the post.