I tried to regenerate lod meshes using tes4ll_midres.bat (and other versions of it), but the only result is that landscape terraforms in a very bad way - meshes missing I guess.

• I don't see Oblivion.esm in your mod list... Therefore you have only the cells which have modifications by mods, not the basic heightmap. One can see this by the yellow area in the heightmap. I think you disabled Oblivion.esm.