awaitで処理が返ってこない

await.cs

private async Task<Message> GetItemIdFromQueue()
{
    AmazonSQSClient client = new AmazonSQSClient( ACCESS_KEY, SECRET_KEY, Amazon.RegionEndpoint.APNortheast1 );
    ReceiveMessageRequest req = new ReceiveMessageRequest();
    req.MaxNumberOfMessages = 1;
    req.QueueUrl = QUEUE_URL;
    
    ReceiveMessageResponse res = await client.ReceiveMessageAsync( req ); // この行
    if ( res.HttpStatusCode != System.Net.HttpStatusCode.OK ) {
        LogError( res.ToString() );
        return null;
    }
}