Why aren't my Shopify products appearing in Shop app search after they used to?

Yeah, start in Shopify admin at Sales channels > Shop > Catalog and check each product's listing status. If it says Ineligible or Prohibited, click it—the status should tell you what's blocking it. For Shop discovery, the item needs to be in Shopify Catalog and have an image, price, and product category, plus meet Shop's merchant rules. Also check that it wasn't changed to Unlisted or given the seo.hidden metafield; either one takes it out of Shop product and store search. If the listing looks fine, test from the customer's actual shipping country/currency: Shop filters results by location and only shows stores that ship there, and results are personalized too. After you fix availability or eligibility, give Shop a few minutes to refresh; store-eligibility changes can take up to 48 hours.