I should also note that when I first noticed the zapper removing the fenugreek smell, I did smell some BO in its place (not a lot), but it went away, eventually.
Herxheimer reactions sometimes occur with zappers, when you first use them, they say. Those might also cause smells, but this should be temporary. I don't think I experienced a herxheimer reaction at all. I used my zapper a lot more than is usually done, though (61 minutes straight on my first try). So, maybe I was zapping during the time when the reaction would have started. I don't know.