co-cluster size zero

[Jayesh-Kumar-Sundaram]

To find the optimal number of co-clusters, I used the coclust.evaluation.internal.best_modularity_partition() function and identified that there are five optimal clusters
code:
int_eval = coclust.evaluation.internal.best_modularity_partition(in_data=data['doc_term_matrix'],
nbr_clusters_range=range(2,50),
n_rand_init=1)

Then when I clustered the data using CoclustMod for 5 clusters I found one co-cluster to be of size (0,0). When I cluster the data to get 2-4 clusters I always clusters which has some size but If I try to get clusters of size >=5, I also end up with only 4 clusters whose size id not (0,0)
code:
model = CoclustMod(init=None, max_iter=20, n_clusters=5, n_init=1, random_state=0, tol=1e-09) #int_eval[0] #Best model
model.fit(X=data['doc_term_matrix'])
plot_cluster_sizes(model)

What is the issue? Why do I get co-clusters of size (0,0). I didn't find the co-cluster size to be (0,0) when I used "CoclustSpecMod" function.