"Electrodes have to be put in the correct place or within 1-2mm, otherwise they can damage a person's speech and balance.
It examined 22 cases involving 21 patients between 2017 and 2019 and found in only three the electrodes were placed in a good position. Five were usable and 13 were ineffective"
I guess the takeaway from this is do your research and then some, on your surgeon.