This problem was reported in this UDN:
1) Launch QAGame with -dx12
2) Open ProcLandscape_Test.umap
3) Enable Show->Visualize->Global DistanceField
Observe random artifacts. The same are not there with DX11 or Vulkan. A quick look in RenderDoc reveals various horizontal and vertical lines in the source GlobalDistanceField<N> textures to the VisualizeMeshDistanceFieldCS shader. In DX11 these textures appear smooth.
There's no existing public thread on this issue, so head over to AnswerHub just mention UE-113387 in the post.