Google's fetch as Google tool in Search Console lets you do a lot of cool things but what happens with the fetch part works but when you also try to render the page, the rendering fails? Barry Adams asked Google's John Mueller this and John responded on Twitter that it means Google was unable to crawl and render the page "within a reasonable time" or Google "can't render it at all."
Here are the errors that Barry noticed where the fetch works but the render has an error:
John said that typically Google is "more patient for indexing" then rendering, which is why this might be the case. So speeding up your pages a bit might help Google also render the page in Fetch as Google.
Here are those tweets:
@JohnMu sorry to bother you but have a question: when a Fetch in GSC works fine, but a Fetch & Render just gives 'Error' for every single page on a site, what could be causing that? pic.twitter.com/FJ8bGgavHQ
— Barry Adams ๐ (@badams) July 25, 2018
Usually, this means we can't crawl/render the page (render w/embedded content) within a reasonable time (live tests have a low timeout to bring results quickly), or we can't render it at all. We're more patient for indexing; you could also check with https://t.co/s55K8LIOKY
— John โ.o(โงโฝโฆ)o.โ (@JohnMu) July 25, 2018
Forum discussion at Twitter.