You need to specify the pH, otherwise this question is difficult to answer.

I am not familiar with the red/ox peaks of BSA at MWCNT-modified GC electrodes, but somewhat at mercury electrodes, so maybe this helps you:

some common peaks are summarized in this article:

https://www.researchgate.net/publication/222139693_The_reduction_of_disulfide_bonds_in_proteins_at_mercury_electrodes

You might find additional information in a later review: https://www.researchgate.net/publication/230001556_Early_Polarographic_Studies_on_Proteins

When looking for Cr ion interactions with BSA and HSA, I also found a specific peak at low potential: https://www.researchgate.net/publication/257575304_Chromium-protein_complexation_studies_by_adsorptive_cathodic_stripping_voltammetry_and_MALDI-TOF-MS

However, at this high potential (I assume that you are still somewhere in the neutral pH region), I am not aware of any studies. But I know that BSA often contains metal impurities and also fatty acid impurities, depending on the route of purification etc., so this might be good to check as well. Since it seems that you first need to oxidize this species (by starting at a higher potential), before you see a reduction peak, it must be a species that is not fully oxidized initially. Does this peak become larger if you hold longer time at the high potential, or have a slower scan rate?

Article The reduction of disulfide bonds in proteins at mercury electrodes

Article Early Polarographic Studies on Proteins

Article Chromium–protein complexation studies by adsorptive cathodic...