Is duplicated by
Changing the quality settings (or having them change on you automatically in the editor) drops mips on landscape heightmap textures, which isn't desirable as it makes it look like there are collision issues as the collision doesn't match the display.
Please exclude TEXTUREGROUP_Terrain_Heightmap textures from the quality setting mip bias. Perhaps there should be an entry in the config file to say whether quality settings can bias them?
From Duplicate Issue [Link Removed]:
When changing the Texture Quality settings through the Engine Scalability settings within the main viewport, the topography/height map of the landscape changes.
The user mentions he originally imported the heightmap from World Machine and were using World Composition. He also found a workaround was to copy the landscape to a new blank map, and then everything worked normally.
The user provided a project with an example landscape displaying the issue. I uploaded and shared this on my drive under the name [Link Removed]
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-11542 in the post.