This question gets asked quite a bit actually, 100% of the time its one of three reasons.

You "created" an order inside your shopify admin, but never "marked order as paid". Draft orders are ignored by our app. The order needs to be "Paid" before it shows up inside the app.

You duplicated the product. Our app only recognizes, originally published products from the app, dups will be ignored.

You added variants to the product OR deleted and re-added variants to the product. When you do this, our app will not see the product anymore, since the variant IDs no longer match the product originally published.