A approval workflow task for approvers to accept/reject which was created 4 months ago, was unable to be open by the approvers, error messages says " you are unauthorized to perform this action" , nothing changed on the workflow settings, is it work as designed?
How to proceed the workflow since it is stuck in the pending for review status.
can you check the approver has access to the site as a whole, even if just "read"? and to the item itself?
This is likely a longshot but I had a slew of these happen after an Active Directory transformation because the account names were transformed. Is it possible the account name has changed in even the slightest way? The way to check is to find the user in a group that is successfully giving him access to content, click on his linked name and is should oppen a window with his account details like the screeshot below.
Next, go into the workflow task and click on the assignee's name and it should open the account details as seen above. Make sure the user account name matches exactly.
I would check to see if the approver has access to the task list associated to the workflow.