Shuttle saw a stock change on an Etsy listing but could not find the Shopify product it is matched to. The stock was not updated in Shopify.
Why it happens
The listing is not matched. Shuttle only updates products that are matched. On the Products page, check whether the listing has a Shopify match.
The Shopify product was deleted. If the matched product no longer exists in Shopify, Shuttle removes the match. Check that the product is still in your Shopify admin.
SKU matching is off, or the SKUs differ. Shuttle can only find the Shopify product by SKU when "Match products and variations by SKU" is on and the SKUs are the same in both shops.
The SKUs are shared. Shuttle does not match by SKU when another Etsy listing uses the same SKUs. It also skips a Shopify product that is already matched to a different listing.
How to fix it
If the product is in Shopify, go to Products, find the listing, open the More actions menu (⋯) and select Match to Shopify. See Matching Products & Variations.
To let Shuttle match by SKU on its own, go to Settings > Products > General, tick Match products and variations by SKU and click Save. Give each variation the same SKU in Etsy and Shopify. Leave this setting off if either shop has duplicate SKUs.
If the product is not in Shopify, transfer it. Go to Products, click Start a bulk transfer and choose Transfer to Shopify. See Transfer products between Etsy and Shopify.
After the product is matched, Shuttle updates its Shopify stock the next time the Etsy stock changes.
Still seeing it?
If the listing is matched and the product is still in Shopify, the error can come from a short problem reaching Shopify. Wait for the next stock change. If the error keeps coming back, contact support and include the product name.