AppSync - An internal failure occurred while resolving this field.

I have an API in AppSync backed by a Lambda resolver that is fetching hierarchical data from AWS Cloud Directory. When I run a deep query with multiple levels and many nodes in the lower levels, I'm getting for some of the fields the following error:

{
      "path": [
        "organization",
        "regions",
        2,
        "stores",
        0,
        "departments",
        5,
        "counters"
      ],
      "data": null,
      "errorType": "InternalFailure",
      "errorInfo": null,
      "locations": [
        {
          "line": 10,
          "column": 11,
          "sourceName": null
        }
      ],
      "message": "An internal failure occurred while resolving this field."
    }

If I use filters and get fewer nodes, the same nodes that failed in the larger query come back without any error. Here is an example of the deeper query (without filters):

query OrganizationUsers {
  organization {
    name
    regions {
      region
      stores {
        store_name
        departments {
          department_name
          counters {
            counter_id
          }
        }
      }
    }
  }
}

I don't have any limits in the API settings regarding the query depth or the resolvers' count.