Imuser

Something seems to be not right with 4.0 upgrade. What happens if you rollback to 3.9? Is it stable?

Nope that won’t, I’ve done that on several of my clients account on Yahoo, it works well.

But as a precautionary measure, its always good to take back up of all the WP files and DB so if somethings breaks, we can restore it back the way it was.

I think you’ve not looked at that WordPress article completely, here is what it says:

NOTE – you should replace all the old WordPress files with the new ones in the wp-includes and wp-admin directories and sub-directories, and in the root directory (such as index.php, wp-login.php and so on). Don’t worry – your wp-config.php will be safe.

So when you download the zip file and unzip it, there is no ‘wp-config.php’ file, there is just a wp-config-sample.php page. More over when you copy the content of unzipped folder and overwrite using FTP, you are just updating the old files in your existing folder with the new files you’ve downloaded from WordPress.

The ONLY thing you should be concerned about is REPLACING entire existing wp-content folder with new one you’ve downloaded, obviously you should never do that as your existing wp-content folder holds your website themes, plugins and other data.

I don’t think its a problem with Yahoo hosting, follow the steps they’ve explained in their help article below to fix the issue:

https://help.yahoo.com/kb/yahoo-web-hosting/SLN25243.html