There are a few possible reasons a SKU could be missing from the Manage Listings page.
1. The SKU is inactive
The Manage Listings page includes your active listings. In other words, searching for an inactive listing will not return search results.
To view the inactive listing, go to Listing > select the marketplace from the menu > search for the SKU.
To activate the listing, click the plug icon located above the listing's image.
Check out Activate Inactive listings for additional details.
2. The SKU is a duplicate
Duplicate listings happen when 2 or more SKUs are assigned to the same ASIN. For example, you sell an item that is both Fulfilled by Amazon (FBA) and Fulfilled by Merchant (FBM). Although the ASIN is the same, the SKUs will be different.
Check out When you have multiple listings under the same ASIN for additional information.
3. The SKU is a brand new listing on Amazon
Listing Mirror syncs with Amazon several times throughout the day. When new listings are added in Seller Central, it can take up to 2 hours for those listings to populate in your Listing Mirror account.
4. The SKU is inactive on Amazon or doesn't have available quantities
Listing Mirror automatically imports listings that are active on Amazon with available quantities. Once a quantity has been added in Seller Central, it will be imported into your Listing Mirror account.
Check out How your listings are imported to learn more about the criteria for importing listings.
5. The SKU is hidden
To view hidden listings on the Manage Listings page, click Filter Results > in the Meets the condition of section, select is hidden > click Save Filters.