Update “Dewey” has just settled down and each time Google do a change, they usually adjust the ranking factors. Example: if your position was based on inbound links, and Google reduced their importance in ranking factors, then a hit would be expected. Similarly if you used paid links – chances are these get hit a bit more every update. *
Trouble is no-one really knows what Google is doing – its all “best guess”. In fact, the update was a bit of a surpprise to many as it was felt that Google had moved toward “everflux”. There’s even a doubt as to whether it was an algo change this time round.
* Interesting footnote for operators maybe: a lot of aff programs have their affiliate and banner links use the casino URL to boost inbounds. Someone suggested that these may possibly now be viewed as “paid links”. It’s possible that that could cause a negative SEO impact rather than a positive one.