User wants to know why approved Sales Order goes back to Pending Approval Status after being edited.
Solution
This behavior is caused by a preference enabled. When the Require Re-approval on Edit of Sales Order preference is enabled, editing an approved Sales Order will cause the Status to revert back to Pending Approval. This preference can be seen by navigating to Setup > Accounting > Accounting Preferences > Order Management > Sales Orders section.
For more information, please see the field level help of Require Re-approval on Edit of Sales Order preference below:
“Check this box to require re-approval when someone edits a sales order that was previously approved.
Note: If you edit a sales order while using a role with permission to approve sales orders, a sales order status is not set to the Pending Approval status.