Different MPC Responses with the Same Input Parameters

I have an MPC in MATLAB with a custom cost function embedded in a script connected to a Simulink model. The issue is that when I change the indexing in the cost function from (1:np) to (2:np+1), I start getting different plots even though the inputs remain the same. What should I add here? I specifically need to use (2:np+1) instead of (1:np).

In my previous work with Particle Swarm Optimization, I faced a similar issue, and adding rng('default') ensured consistent results. However, that approach doesn’t seem to work here.