use mvnrnd to generate random numbers

I want to use mvnrnd to generate random numbers with a multivariate normal distribution. However, I get an error saying "sigma must be a symmetric anti-positive matrix" and cannot execute it. Even if we confirmed the covariance, the value was semi-positive including 0, and we also confirmed that it was symmetric using issymmetric. I checked it many times and got an error even though it was a symmetric definite matrix. I would like to know the solution.