Work item cannot be executed in status STARTED

Hi,

I am facing an issue in which the workflow stays is "In process" status.

We are trying to post a document through tcode FBV3. After the approver approves the document, the document should get posted. But the work item of the document stays in "In process" Status.  In the step history tab, i can see the message - Work item XYZ cannot be executed in status STARTED.

This is happening for many documents. I do not understand the reason for it.