Rank Position Test
This may affect rank when your website is being placed in higher rank positions than it may have ‘earned’ through SEO, but when Google’s algorithm thinks that your content ‘might’ have greater appeal to users.
Yes, I am suggesting that Google does tests on rank positions to ‘feel out’ the market response. This only works to the positive unless you are not the site being tested and happen to be near the bottom of page 1 in search results – losing you spot when the test is active.
It comes down to Google saying to itself: “I wonder what happens if we try this…?”
This test may also occur when your website is on the cusp of a ‘switching factor’ in your genre like with local search, where the search results become temporarily localized (show map listings in SERPs)
Or vice versa of course.