Missing listings are a side effect of orders which contained an item SKULabs has not received in a listing sync from your channel. You have several options to resolve this either on your store, or on SKULabs.
Run a listing sync for the affected store to see if the item has been added recently and just needs to be imported.
If this doesn't work, check the order on your store to see if the item was deleted or deactivated. If this is the case, either reactivate the item or edit the order on your sales channel to change the item that should be included on the order, then re-sync your orders to fetch the update in SKULabs.
Also read our guide on troubleshooting missing listings.