The behavior in this bug is a little odd since it is not present in any project that is upgraded to 4.24.1 (CL-10757647), but only those that are created directly in 4.24.1. The behavior is also a little different in 4.25 (CL-10870012), being that only the Grass physics material is recognized on the Landscape.
Results: When walking over the landscape Default prints, but if you try walking over the static meshes it works as expected.
Expected: Landscape return correct surface type
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-86165 in the post.