Stateful predict block failed to evaluate mask initial commands

I see the issue now. The Stateful Predict block can only work with the modern framework in Deep Learning Toolbox (not the network object). One option might be to retrain the model by building it using layers in the Deep Network Designer app and using the trainnet function. If you wish to continue using the model you have trained as is, you may want to explore if using the gensim function succeeds at generating Simulink blocks for your network.