Sergy XYZ

Hi folks, I made an animation using a character rigged and with hair that was provided by my client (I did not create it). For some weird reasons, when I render the animation at some point the hair look relevantly changed, having some very weird dark spots on it and the "seed" of the hair seem to change as well. I did not animate any of the hair values. Does anyone have any idea of what this could be? I am going crazy and need to deliver this today 😞