Appsync GSI not producing existing DynamoDB record by Graphql using amplify

I've used Amplify to generate AppSync schema and GraphQL resolvers automatically. All of sudden, a major fetch stopped working. This is the query that I am running in the AppSync console:

query CreamByUuid {
  creamByUUID(streamUUID: "6e1a5555-9999-6666-84c1-54e777777777", id: {}) {
    items {
      id
    }
    nextToken
  }
  milkBySlug(slug: "cherry-rare-solo-appearance") {
    nextToken
    items {
      price
      id
    }
  }
  getCream(id: "77bababa-8888-3333-bb2b-857c470d5555") {
    id
    creamUUID
  }
}

The first part is a GSI that fetches a stream by a field called the “creamUUID”. The problem is, the result returns an empty array:

{
  "data": {
    "creamByUUID": {
      "items": [],
      "nextToken": null
    },
    "milkBySlug": {
      "nextToken": null,
      "items": [
        {
          "price": 7,
          "id": "17e50e71-ay7d-8382-1098-25c616444444"
        }
      ]
    },
    "getCream": {
      "id": "77bababa-8888-3333-bb2b-857c470d5555",
      "creamUUID": "6e1a5555-9999-6666-84c1-54e777777777"
    },
  }
}

I’ve tested another GSI, milkBySlug, to make sure it’s not a broader GSI issue. As you see though, I am correctly getting an item back.

More troubling, when I fetch the Cream by its ID, I actually get the Cream record back (“getCream” returns the record with a creamUUID of “6e1a5555-9999-6666-84c1-54e777777777”)

So the Cream record exists in DynamoDB, and a direct query of it using an ID returns it. But a GSI creamByUUID with the creamUUID returns an empty array.

The resolver is autogenerated by amplify push, and I can share that if it is helpful. The queries I’m making are directly within the AWS console, so it can’t be a coding error on my part…

Can anyone help? I'm out of ideas about why the creamByUUID returns an empty array when it should return the Cream record with ID 77bababa-8888-3333-bb2b-857c470d5555