I wonder if it has something to do with size and the strength of the sites ranking.
Both of my sites were built the same way (handcoding) and both were vulnerable to hijacking in terms of how I did my linking.
Somehow the Bourbon update plunged the smaller site while the larger one is still #1 for several related 2 word searches and even #7 for a general one word description. It's been there for a couple of years at least.
One possible factor is that the site that was spared is about 9 years old while the smaller one is about 5 years old.
I'd be interested in theories on what saved the larger site while the smaller one dropped significantly.
I'm gong to wait a bit to see if the damaged site comes back. If it doesn't I'll close it down and put some of the best articles on the other site, mainly those written by experts in the field.
I'm also concerned about protecting the larger site that survived Bourbon. This update had made me realize how vulnerable my sites are.