Amazon Neptune Serverless LOAD_UNEXPECTED_ERROR

Has anyone experienced an issue like this when executing a load job on a Neptune serverless instance configured to scale from 1 to 32 NCUs? This load seems to have failed with an unexpected error, but all of the error indicators in the status response below show that there were no errors. It also seems like the load never actually started as the only entry in the feedCount element is LOAD_NOT_STARTED.

I had previously loaded a few billion vertices successfully, but am having trouble loading the edges. I am attempting to load all OpenCypher formatted .gz files in a given S3 prefix. If I change the launch request to specify the first file in the prefix, it does load fine and complete without error. However, I get the status response below after about 7.5 hours when attempting to load all the files at once.

Is there any way for me to get more details on what the possible failure might be?

{
    "status" : "200 OK",
    "payload" : {
        "feedCount" : [
            {
                "LOAD_NOT_STARTED" : 3171
            }
        ],
        "overallStatus" : {
            "fullUri" : "s3://my-bucket/neptune/data/edge",
            "runNumber" : 1,
            "retryNumber" : 1,
            "status" : "LOAD_UNEXPECTED_ERROR",
            "totalTimeSpent" : 26754,
            "startTime" : 1692320967,
            "totalRecords" : 0,
            "totalDuplicates" : 0,
            "parsingErrors" : 0,
            "datatypeMismatchErrors" : 0,
            "insertErrors" : 0
        },
        "errors" : {
            "startIndex" : 0,
            "endIndex" : 0,
            "loadId" : "637f253f-f0ef-419e-a8b6-599eceea2222",
            "errorLogs" : [ ]
        }
    }
}

I launched the load job with the following command:

curl -X POST https://neptune-dev-1.cluster-cwcwpnhm4dly.us-east-1.neptune.amazonaws.com:8182/loader \
  -H 'Content-Type: application/json' \
  -d '{
        "source" : "s3://my-bucket/neptune/data/edge",
        "iamRoleArn" : "arn:aws:iam::<accountId>:role/NeptuneLoadFromS3",
        "format" : "opencypher",
        "region" : "us-east-1",
        "failOnError" : "TRUE",
        "parallelism" : "OVERSUBSCRIBE",
        "userProvidedEdgeIds": "FALSE"
      }'

Thanks for reading! Paul E.