Wordpress Multisite Installation Error
I've seen this happen when there's a permission issue on the version-info-cache.json file that prevents the upgrader from properly deleting it.  The file can be found in your CiviCRM "Temporary Files Directory".  

If you're not sure where to find your Temporary Files Directory, you can check at Administer menu » System Settings » Directories.  If there's a token (e.g. [civicrm.files]/upload), you can see the value of the token by pressing the "help" icon (see screenshot below).

Try deleting version-info-cache.json manually (e.g. via FTP or CPanel File Manager).  Then visit the Civi System Status Page (Administer menu » Administration Console » System Status) and the issue should clear up.

This file is also auto-deleted every three days - so if this seems like a lot, simply ignore it!