Can you please give some more information regarding this, e.g. configuration or screenshot..
Can't think of any reason behind this error.
Please find the screenshot below
When i try to open the Completed or running Nintex workflow i get the following the error in O365 sharepoint Site..
Had you check your logs?
And did you try with SharePoint Designer to publish a simple workflow to see whether the workflow service still running properly?
thanks for your reply siang chew, the problem in sharepoint site so i raise a ticket in MS support,they made one patch now it's working as i expected..