For one e-commerce website, in place of the proper meta description, Google is showing a 318-character-long mix of snippets from the homepage content for the domain search (e.g. [example.com]). A brand search returns the correct meta description - as do the keywords the homepage ranks for.
I know Google changes the meta description if it doesn't think it's relevant, but this one (there is only one) is and has (as far as we know) shown until now, and I've never seen such a mix of text in the SERP, and so many characters - it's picking up random text from bits of anchor text e.g. "privacy policy", title attributes from links, labels from radio buttons and more.
The home page W3C validates apart from a couple of basic things like missing alt text. The only things that might be related that don't are some custom meta name tags added by the CMS - but I wouldn't think this would make any difference to whether a meta description is displayed properly or not?
I've recommended we wait until tomorrow to see if Google fixes this on recrawl, but does anyone have any ideas if it doesn't? The homepage doesn't feature much standalone text, so I was thinking if we add a few extra words it might encourage Google to pick from that if it doesn't want to use the meta description. The text would have to be useful for users and fit in with the design of course, which could be awkward...