gromov_barycenters function always returns the zero matrix

Describe the bug

gromov_barycenters function always returns the zero matrix as cost matrix.
I executed the code below multiple times and it always returns 0.

Screenshots

Code sample

from ot.gromov import gromov_barycenters

n = 5
g1 = nx.erdos_renyi_graph(n,.8)
g2 = nx.erdos_renyi_graph(n,.8)

c1 = nx.adjacency_matrix(g1).toarray()
c2 = nx.adjacency_matrix(g2).toarray()
print(c1)
print(c2) 
b , log = gromov_barycenters(n,[c1,c2] ,log = True )  
print(b)
print(log)

Expected behavior

A non zero matrix.

Environment (please complete the following information):

OS (e.g. MacOS, Windows, Linux): MacOs , also tried on collab
Python version:Python 3.11.5
How was POT installed (source, pip, conda): pip

Output of the following code snippet:

import platform; print(platform.platform())
import sys; print("Python", sys.version)
import numpy; print("NumPy", numpy.__version__)
import scipy; print("SciPy", scipy.__version__)
import ot; print("POT", ot.__version__)

macOS-12.5.1-arm64-arm-64bit
Python 3.11.5 (main, Aug 24 2023, 15:09:32) [Clang 14.0.0 (clang-1400.0.29.202)]
NumPy 1.26.0
SciPy 1.11.3
POT 0.9.1