Recently, We patched one of our SharePoint 2013 environment and ran SharePoint products configuration wizard without any issues. However, we noticed that the server status is still in “Upgrade Available” for SharePoint application & Web front end server from Central Administration > System Settings > Manage servers in this farm page. Ideally the server status should read “No action required” if everything goes good.
The “Upgrade available” simply means that there is a newer patch available at the SharePoint Updates page than the one installed on your SharePoint farm. We checked the Farm version and made sure its the latest available version.
Found this issue is related to either some content databases/sites which still need an upgrade!
Run: stsadm -o localupgradestatus from any of your server stating the “Upgrade Available” status. You should get a summary like:
 content database(s) encountered.
 content database(s) still need upgrade or cannot be upgraded.
 site collection(s) are contained in the content databases.
 site collection(s) still need upgrade.
 other objects encountered,  of them still need upgrade or cannot be upgraded.
Based on the summary, you have to either upgrade your SharePoint database or sites (Upgrade-SPContentDatabase, Upgrade-SPSite). Once done with your site or database upgrade, run PSConfig wizard again.