Cached links missing - on just some search results

[glitterball]

I've noticed lately that the "cached" link is missing from some pages in the results, but present for the same page if I perform another query.

example: The results from a search for "blue widget" omits the "Cached" link beside bluewidgets.com (only the "Similar" link is present).
However, if I search for "blue and pink widgets", the "cached" link is present beside the very same result - "bluewidgets.com".

None of the sites are using noArchive.

It's happening for some of my sites and a couple of competitors as well - Any ideas?

[tedster]

I've been seeing cache links come and go without obvious pattern for a while now. If I had to guess, I think it may have something to do with a recent crawl that retrieved something other than a 304 Not Modified response.

The Google cached pages update more slowly than the new crawl data gets processed for the SERPs. They'd want to be sure that the search results were based on the content of the cached page that they show. Or so I presume.