Runge Kutta Divergence

I'm trying to solve a system of differential equations in order to optimize a certain design. I already had a program based on Runge-Kutta and it was working fine. After the inclusion of more variables in the equations, I was faced with the problem that the output of the Runge-Kutta algorithm diverges sometimes. I checked the equations many times and I'm quite certain there's nothing wrong with them, and the new system converges correctly for some values, so I have no idea what I can do to fix this divergence issue.
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