I reported this as a but to Nintex.  I have to run to a meeting, but when I get back I'll post the case number.  They confirmed it was a bug.  I have the same version Nintex that you have.  I have to build my link before the Task now, then insert it as a variable into the Task.

Ok, here are the details.  I reported the issue on February 6th, 2017.  Case number: 00139406 Subject: Flex Task Notification Doesn't Display Item Name after being edited.  It was reported as a bug and sent to the developers on the 13th.  Haven't heard anything since then.  I'm going to send a follow up email.
 

   hello, i have the similler problem.. wondering if you have heard back from them yet. 

Hi Prasad,

This morning I heard from a colleague here at work that a new Nintex Workflow update/fix package has been released which resolves this and other issues. See the release notes:

https://community.nintex.com/docs/DOC-1153-nintex-workflow-2013-release-notes

Bug Fixes - The following issues are corrected

• Corrected the display of question marks in the name of a managed holiday in Russian site settings (44511)
• Corrected the license attributions notice for react JS in NW2016 (54857)
• Corrected the loss of the Workflow Description when Publishing a Workflow (55736, 61256)
• Corrected the loss of workflow conditions when a workflow is published and reopened (58666)
• Corrected the failure to start on item modification of a Reuseable Workflow when associated with a Content Type (59273)
• Rectified the multiple addition of line breaks when editing the source HTML in Send Notification (59600)
• Corrected an issue when using a variable in the reftext in a hyperlink (61258)
• Corrected the ability to view workflow history of a workflow created with a Site Collection Reusable Workflow (61723)
• Corrected a issue with the hyperlink in Send notification reverting to the column name of the reference (61726)
• Corrected the Task Description field for Assign a Task action not showing rich text formatting (61997)
• Corrected a translation error in Create Appointment in German sites (62003)
• Corrected the Context item display name not resolving the item name when the task emails are sent to the assignee (62006)
• Corrected the unwanted rounding of numbers in document generation for MS Word and PowerPoint - correct in Excel(62202)
• Corrected the missing or incorrect labels in Administration reports (62216, 62217)
• Corrected an issue with the Send Notification email body that changes when Edit HTML dialog is opened and closed(62254)
• Corrected an issue with conditional start configured for a change from previous value(62256)
• Corrected and issue with the Export to Excel reporting webpart only exporting data from the current site and not other sites(62536)
• Corrected an issue with Enterprise reports not sorting properly and excel export is not working for all sites (62590)
• Corrected the splitting of results when exporting to Excel using the Nintex Workflow reporting web part on large content databases(62599)
• Corrected an issue with Administration reports missing internal resource data(62631)

Thank you very much for the reply! Can you help me to understand if we can install this new update on August 2016 SP 2013 CU?