Open Portal Tasks using processTasklink() function in site

Currently I am working on 17.2 and created a process report in my site and trying to open portal tasks from a!processtasklink() function in a grid field.But every time I open the task it shows me error: The task has been deleted or completed by another user. But the portal task is still in active state and I am able to access it from /designer.

Do we have any other approach through which we can access portal tasks rather tempo tasks while clicking on task link in grid field? 

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