If an order was shipped before its items were scanned, for example after bulk shipping, the order still has unverified items from past shipments. You can verify (clear) those items afterward, without creating a new shipment.
How to clear a shipped order
Open the order. Scan its packing slip, or go to Orders, open the Shipped tab and click the order number.
Verify the items in one of two ways:
Scan each item's barcode, the same way you do when picking.
Or, in the blue Recommended notice at the top of the order ("Click here to bulk verify N unverified items from past shipments"), click bulk verify to verify all of them at once.
If your inventory uses per-scan deduction, verifying these items is what deducts them from stock. See How to deduct orders in SKULabs.
How to find shipped orders with unscanned items
On the Shipped tab, click Menu and select Un-scanned items report. Choose a date range to see which items were shipped but not scanned.
A safer workflow
Tip: Shipping before scanning means labels are printed and your sales channel is notified before you know every item is in stock and packed. Where possible, scan and verify items first, then ship. If you need to hold tracking until orders are checked, see How to hold and release shipment notifications with "Release orders upon scan".