prediction results are not consistent

Hi, I'm using alphafold2 to predict my protein structure. I found the result models always different no matter for x y z coordinates or plddt even I used the exactly same command line and didn't change any parameter. Sometimes I can even see the 3d structure difference in the visualization.
Could you explain the reason of the variance?
I want to use alphafold to predict the structure for different mutations, so the variance is important to me.