The page I'm trying to fetch is public.  The server logs show no request.  Google reports that any page on my site is Temporarily unreachable. It won't even fetch the verification file, a static HTML file that was successfully used to verify with the webmaster tool application itself. My site is running on the Google app engine.What is causing this?
Temporarily unreachable when using fetch as Googlebot from Webmasters Tools
google search console;google app engine;fetch as google
According to Google, it's because:Fetch as Google can't currently fetch your URL because the server took too long to reply.Or Fetch as Google cancelled your fetch because too many consecutive requests were made to the server for different URLs.I've witnessed this happening a few times in the past. More often than not, it's an intermittent problem that goes away after a short period of time.Important note:Note the URL is not unreachable for all of Google - It is just  unreachable for the Fetch as Google simulation tool.