Fuzzy C-means : All clusters centers converge to the same point after the first centroids update

I am implementing Fuzzy C-means to work with image segmentation following the given algorithm :

However when updating the centroids (this is the first thing that I do) all clusters centers converge to the very same point, here is my code:

Initializing centroids to random points in the image, points are different from each others.

for(int j=0; j<c; j++) {
    vertex pixel = vertices[rand()%n];
    while(!far(pixel, assigned)) pixel = vertices[rand()%n];
    add_element_list(assigned, pixel);
    centers[j].r = pixel.r; centers[j].g = pixel.g; centers[j].b = pixel.b;
    centers[j].a = pixel.a;
}

Updating clusters centers

for(int j = 0; j < c; j++) {

    double numeratorR = 0.0, numeratorG = 0.0, numeratorB = 0.0, numeratorA = 0.0;
    double denominator = 0.0;

    for(int i = 0; i < n; i++) {

        double weight = fmax(pow(U[i][j], FUZZINESS), EPSILON);

        numeratorR += weight * (vertices[i].r);
        numeratorG += weight * (vertices[i].g);
        numeratorB += weight * (vertices[i].b);
        numeratorA += weight * (vertices[i].a);
        denominator += weight;
    }
    
    denominator = fmax(denominator, EPSILON);

    centers[j].r = numeratorR / denominator;
    centers[j].g = numeratorG / denominator;
    centers[j].b = numeratorB / denominator;
    centers[j].a = numeratorA / denominator;
}

Initialize each point membership to each cluster, this is done before updating the clusters

void initialize_membership_matrix(double** U, int n, int c) {

  srand(time(NULL));

    for(int i = 0; i<n; i++) {
        double sum = 0.0;

        for(int j = 0; j<c; j++) {
          
            U[i][j] = (double) rand() / RAND_MAX;
            sum += U[i][j];
        }

        for(int j = 0; j<c; j++) {
            U[i][j] /= sum;
        }
    }
}

For instance all clusters centers converge to RGB(117,225,14) after the cluster update, and this point change for each image.

I though it would be a problem with my random initialization of centers clusters but even with the 'far' option in the code I have the same issue. Then I also though of how random I initialize membership matrix in the first place (is C random very random in this case? I have over 600k pixels of data).

Thank,