When a landscape uses simple collision, the returned physical material can be mismatched.
This seems to be a result of ConvertHeightfieldDataForPhysx within ULandscapeHeightfieldCollisionComponent::CookCollisionData not offsetting DominantLayers by NumSamples for simple collision leading to a material mismatch.
Open the advanced vehicle template project.
Set the landscape's simple collision mip level to 5.
Perform a pair of line traces, one complex and one simple, against the landscape's desert area and note the returned physical materials are different.
Perform the same traces again, this time against the landscape's track area and again not that the returned physical materials are different(and switched).
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-81956 in the post.