I changed out one of my affiliate links, in my php redirect file, using a new parameter name for the new link. I deleted the old parameter. The page that I link from dropped an average 250 positions since the change (last Thursday). My site only has 2 different affiliate links (that can be found on just 3 pages out of over 100), so I don't consider it "thin affiliate" but it would appear that Google didn't like the addition of the new link with a new redirect parameter. It could be an overlap period (while the old link gets purged and the new one becomes accepted).