Something's weird. How many downloads did you get on the bookbub? You don't have to answer that, but it must have been a couple of thousand right? And only 5 also boughts? On a book that has over 600 reviews so it must have been bought thousands and thousands of times? Which would generate a lot of also boughts?
Was the bookbub free if you don't mind my asking? Or 99 cents?
Edit - I just checked. My WW II historical fiction right now has three pages, all appropriate, but the day it launched it had 29 pages of also boughts, based on the preorders alone, which were only I think 29 or so. Maybe it was your bookbub that messed it up, or maybe it was just a coincidence and Amazon changed something, badly.