Comment on April 2017 CU for SharePoint 2013 product family is available for download by Stefan Goßner

Hi Vinay,
this is not a problem with SharePoint but with the cached MSI files used by the installer to maintain product installations and updates. If files are missing from this cache no further updates can be installed.
In worst case this requires to reinstall the machine. You can also open a support ticket to help analyzing the issue to see if and how the cache can be fixed.
See here for details: https://blogs.msdn.microsoft.com/heaths/2006/11/30/rebuilding-the-installer-cache/
Cheers,
Stefan