Mesh generation algorithm gives visual artifacts

Right now I am trying to implement terrain generation. I am using msvc visual studio 2019. And when I got to decreasing level of details in my function, generation started to be very glitchy. Everything is fine when I am not using any of level of details decreasing values. But everything changes after 1 and more - generation starts to be glitchy and generates atifacts. Here is some examples.

This one is correct as it should be. In my function this stands for parameter 0 in LevelOfDetails.

And Incorect examples. LevelOfDetails=1:

LevelOfDetails=3-6:

This is a function for generating meshes:

static void
GenerateTerrainMesh(world* World, noise_map* NoiseMap, float HeightMultiplier, int LevelOfDetail)
{
    int Width  = NoiseMap->Width;
    int Height = NoiseMap->Height;
    //float TopLeftX = (Width - 1)  / (-2.0f);
    //float TopLeftZ = (Height - 1) / ( 2.0f);

    if(LevelOfDetail < 0) LevelOfDetail = 0;
    if(LevelOfDetail > 6) LevelOfDetail = 6;

    int SimplificationInc = (LevelOfDetail == 0) ? 1 : (LevelOfDetail * 2);
    int VerticesPerLineX  = (Width  - 1) / SimplificationInc + 1;
    int VerticesPerLineY  = (Height - 1) / SimplificationInc + 1;

    InitializeMeshTerrain(World, VerticesPerLineX, VerticesPerLineX);

    int VertIndex = 0;
    int TrigIndex = 0;
    for(int Y = 0; Y < Height; Y += SimplificationInc)
    {
        for(int X = 0; X < Width; X += SimplificationInc)
        {
            World->Terrain.Vertices[VertIndex] = V3((float)X, HeightMultiplier * HeightFlatten(World->NoiseMap.Values[Y*World->NoiseMap.Width + X]).y * HeightMultiplier, (float)Y);
            World->Terrain.UVs[VertIndex]      = V2(X/(float)Width, Y/(float)Height);

            if((X < (Width - 1)) && (Y < (Height - 1)))
            {
                AddTriangle(World, &TrigIndex, VertIndex, VertIndex + VerticesPerLineX + 1, VertIndex + VerticesPerLineX);

                AddTriangle(World, &TrigIndex, VertIndex + VerticesPerLineX + 1, VertIndex, VertIndex + 1);
            }

            VertIndex += 1;
        }
    }
}

And helper functions, but there should not be any errors:

static void
InitializeMeshTerrain(world* World, int Width, int Height)
{
    World->Terrain.VerticesCount = Width * Height;
    World->Terrain.FacesCount    = (Width - 1)*(Height - 1)*2;
    World->Terrain.UVCount       = Width * Height;

    World->Terrain.Faces    = (face*)malloc(sizeof(face)*World->Terrain.FacesCount);
    World->Terrain.Vertices = (v3*)malloc(sizeof(v3)*World->Terrain.VerticesCount);
    World->Terrain.UVs      = (v2*)malloc(sizeof(v2)*World->Terrain.UVCount);
}

static void
AddTriangle(world* World, int* Index, int a, int b, int c)
{
    World->Terrain.Faces[*Index].a = a;
    World->Terrain.Faces[*Index].b = b;
    World->Terrain.Faces[*Index].c = c;

    *Index += 1;
}

What problem could be there? Thank you. UPD: I added some additional data to work with such as Mesh Data and Vertices Data for each LevelOfDetail:
Correct:
LevelOfDetail=0
Incorect 1:
Incorect LevelOfDetail=1
Incorect 4:
Incorect LevelOfDetail=4
Incorect 6:
Incorect LevelOfDetail=6