A new update is available (8.1.4 for example) but the admin sections still shows an older version (8.1.3 for example) as the latest version.
The updater app as well as the admin backend are checking an URL which returns the current version. If this URL returns the 8.1.3 and not the 8.1.4 in the example above you need to be patient until the updater URL has been updated.
If you want to check which version the updater URL is returning you can do this manually:
which returns the version 8.2.1 as the latest version.
The values are:
8x0x0x7 = The ‘version’ number in your config.php, here for example 8x0x0x7 (points are replaced by x)
stable = The “release” channel with the four possible values “stable”, “production”, “daily” and “beta”.