Issue
When approving a task, the approver is redirected to the SharePoint task item rather than the ApproveReject.aspx page.
Resolution
Run the following NWAdmin.exe command to reassociate the correct ApproveReject.aspx page.
nwadmin.exe -o settaskform -siteurl "http://yoursitecollection" -contenttype "Nintex Workflow Task" -taskformurl "_layouts/nintexworkflow/ApproveReject.aspx" -updatechildren yes
More information on the use of the NWAdmin tool can be found in our guide attached below.
Additional Information
The correct Nintex ApproveReject.aspx page has not been associated to the task content type.