We have had essentially the same thing happen. Three times now in 18 months. The rep says 4 of the 8 electrodes are still working, the other four are not. The cause: "probably" the lead has moved. No x-ray yet, but "probably next time." There has been no mention of surgery to correct it, although I expect that will be the case in the near future.

Not at all what you (or I) wanted to hear.