When removing a Page Workflow and adding a new one to a document, if the new workflow uses the same workflow states as the old workflow and the workflow events and actions history (document activity) was retained, the document is automatically moved to the current state of the page with the old workflow.
However, if the page had an approval process running before changing the workflow to the new one, a user who is already assigned as a reviewer does not change unless the page is transitioned. The workflow transition causes the approvers/reviewers to be refreshed with the new user values for reviewers added to the new workflow.
In the following example, the user ‘Ashley’ was automatically added as an approver in the Review state
Now, If the already running workflow is modified with another approver, the page needs to be updated for the approval user to change.