To be fair, yeah, I’d lean more “wobble” than some grand mystery, but I wouldn’t trust Google to say anything useful about it either. If it’s a couple affiliate pages only and the rest of the site is basically normal, I’d check the usual boring stuff first: which queries dropped, whether it’s desktop/mobile split, and if the URLs actually changed position or just lost impressions. I’ve had pages look dead in GSC and then come back a few days later without me touching anything. If it keeps sliding for more than a week, then yeah, start looking at internal links, cannibalization, and whether one page got a small boost by stealing the same intent. That “one page up, rest down” pattern usually isn’t random random. It’s just Google being annoying about which page it thinks deserves the slot. Could be wrong though.