[POT] ot.emd limitations on matrix size

Hi, I'm trying to use the ot.emd function to solve for a 3000 x 5000 transportation problem, but I get all zeros for the solution. It works if I take a subset of, say, 1000 x 1000. Do anybody know what are the matrix size limitations for this function? Is it expected to handle matrices of these sizes? Thanks, Vanessa