C++/Raylib - Unable to load mesh with Assimp

Question

I want to preload 3d obj files before I run InitWindow from Raylib by preloading with assimp. So I have the following code:

std::vector<Mesh> preloadedMeshes;    // Store preloaded meshes
std::vector<Model> terrainTiles;      // Models created from the preloaded meshes

// Function to load meshes with Assimp
Mesh LoadMeshWithAssimp(const std::string& filePath) {
    Assimp::Importer importer;
    const aiScene* scene = importer.ReadFile(filePath, aiProcess_Triangulate | aiProcess_FlipUVs);

    if (!scene || !scene->HasMeshes()) {
        throw std::runtime_error("Failed to load mesh: " + filePath);
    }

    aiMesh* ai_mesh = scene->mMeshes[0]; // Assume a single mesh for simplicity

    Mesh mesh = { 0 };
    mesh.vertexCount = ai_mesh->mNumVertices;
    mesh.triangleCount = ai_mesh->mNumFaces;

    // Allocate and copy vertex positions (CPU memory)
    mesh.vertices = (float*)MemAlloc(mesh.vertexCount * 3 * sizeof(float));
    for (unsigned int i = 0; i < mesh.vertexCount; i++) {
        mesh.vertices[i * 3 + 0] = ai_mesh->mVertices[i].x;
        mesh.vertices[i * 3 + 1] = ai_mesh->mVertices[i].y;
        mesh.vertices[i * 3 + 2] = ai_mesh->mVertices[i].z;
    }

    // Allocate and copy normals (CPU memory)
    if (ai_mesh->HasNormals()) {
        mesh.normals = (float*)MemAlloc(mesh.vertexCount * 3 * sizeof(float));
        for (unsigned int i = 0; i < mesh.vertexCount; i++) {
            mesh.normals[i * 3 + 0] = ai_mesh->mNormals[i].x;
            mesh.normals[i * 3 + 1] = ai_mesh->mNormals[i].y;
            mesh.normals[i * 3 + 2] = ai_mesh->mNormals[i].z;
        }
    }

    // Allocate and copy texture coordinates (CPU memory)
    if (ai_mesh->HasTextureCoords(0)) {
        mesh.texcoords = (float*)MemAlloc(mesh.vertexCount * 2 * sizeof(float));
        for (unsigned int i = 0; i < mesh.vertexCount; i++) {
            mesh.texcoords[i * 2 + 0] = ai_mesh->mTextureCoords[0][i].x;
            mesh.texcoords[i * 2 + 1] = ai_mesh->mTextureCoords[0][i].y;
        }
    }

    // Allocate and copy indices (CPU memory)
    mesh.indices = (unsigned short*)MemAlloc(mesh.triangleCount * 3 * sizeof(unsigned short));
    for (unsigned int i = 0; i < mesh.triangleCount; i++) {
        mesh.indices[i * 3 + 0] = (unsigned short)ai_mesh->mFaces[i].mIndices[0];
        mesh.indices[i * 3 + 1] = (unsigned short)ai_mesh->mFaces[i].mIndices[1];
        mesh.indices[i * 3 + 2] = (unsigned short)ai_mesh->mFaces[i].mIndices[2];
    }

    return mesh; // CPU-side Mesh, not yet uploaded
}



// Preload meshes before initializing OpenGL
void PreloadMeshes() {
    try {
        preloadedMeshes.push_back(LoadMeshWithAssimp("resources/models/Farabale_0.obj"));
        preloadedMeshes.push_back(LoadMeshWithAssimp("resources/models/Farabale_1.obj"));
        preloadedMeshes.push_back(LoadMeshWithAssimp("resources/models/Farabale_2.obj"));
        preloadedMeshes.push_back(LoadMeshWithAssimp("resources/models/Farabale_3.obj"));
    } catch (const std::exception& e) {
        TraceLog(LOG_ERROR, e.what());
    }
}

// Upload meshes to GPU and create models
void CreateModelsFromMeshes() {
    for (auto& mesh : preloadedMeshes) {
        UploadMesh(&mesh, true);  // Upload the mesh to GPU
        Model model = LoadModelFromMesh(mesh);
        terrainTiles.push_back(model);
    }
}

And if I do the following:

const int screenWidth = 1280;
const int screenHeight = 720;
Vector3 unityPosition = (Vector3){-189.29, 105.66, 68.22};
PreloadMeshes();
InitWindow(screenWidth, screenHeight, "Dear ImGui Raylib(OpenGL) example");
CreateModelsFromMeshes();

I can see very weird obj files loaded. Take a look:

But if I comment out and call loading of obj by the LoadModel function provided from raylib I see the scene perfectly fine:

PreloadMeshes();
InitWindow(screenWidth, screenHeight, "Dear ImGui Raylib(OpenGL) example");
//CreateModelsFromMeshes();

terrainTiles.push_back(LoadModel("resources/models/Farabale_0.obj"));
terrainTiles.push_back(LoadModel("resources/models/Farabale_1.obj"));
terrainTiles.push_back(LoadModel("resources/models/Farabale_2.obj"));
terrainTiles.push_back(LoadModel("resources/models/Farabale_3.obj"));

Produces this:

So as you can see no weird artifacts. Why is that? What am I doing wrong with Assimp ?