We are all looking forward to the mobile friendly algorithm being released by Google on April 21st, and with that comes a lot of preparation. Some of the tools being used are Google's mobile testing tool and the mobile usability reports within Google Webmaster Tools.
But both tools show different things to webmasters, the big question is if you pass the test at the Google mobile friendly testing tool but see some errors in the Google Webmaster Tools Mobile Usability reports, do you need to take action?
I recently made one of our websites (ShulCloud) mobile friendly, it was officially on March 11th. Here is a picture of the desktop and mobile versions:
After we launched the new mobile version, we tested it in the mobile tool from Google and it passed. But Webmaster Tools still showed errors. I checked this morning again and the errors are starting to drop down and you can see, it is delayed by a few days - it says March 21st is the last time it updated:
The big question many webmasters are asking is if we pass the Google mobile friendly testing tool but see errors in Google Webmaster Tools Mobile Usability reports are we still at risk of not ranking well in the mobile results after April 21st?
I think the best check is to ensure your site has the mobile friendly label and if you do, then I think you should be okay for now.
I will try to confirm this but I am fairly confident I am correct. :)
Forum discussion at Google Webmaster Help.
Update: John Mueller from Google sent me this statement on Google+:
The mobile usability report has dates, so you can kinda see where those issues are coming from. We do have to recrawl & reprocess the URLs when you make changes, so I'd make sure you're letting us know about that through a sitemap file, for example. In general, I'd focus on the mobile-friendly-test when it comes to these issues, but ... the other tools sometimes bubble up additional issues that are worth cleaning up (even if they don't affect the mobile-friendly label).
You also need to watch out for issues like which might not be directly visible in a per-URL test (for example, if the equivalent for a desktop page with normal content is an error page that's mobile-friendly, then that's still not a proper mobile version of a page).
Update: Here is the answer to the question, in short, I was right above.