Reading non-existent documents while debugging is very slow

CosmosDBDebugIssue.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netcoreapp2.1</TargetFramework>
  </PropertyGroup>

  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|AnyCPU'">
    <LangVersion>latest</LangVersion>
  </PropertyGroup>

  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'">
    <LangVersion>latest</LangVersion>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.Azure.DocumentDB.Core" Version="1.9.1" />
  </ItemGroup>

</Project>

Program.cs

using System;
using System.Diagnostics;
using System.Net;
using System.Threading.Tasks;
using Microsoft.Azure.Documents;
using Microsoft.Azure.Documents.Client;

namespace CosmosDBDebugIssue
{
    internal class Program
    {
        private static async Task Main(string[] args)
        {
            const string serviceEndpoint = "https://localhost:8081/";
            const string accountKey = "C2y6yDjf5/R+ob0N8A7Cgv30VRDJIWEHLM+4QDU5DE2nQ9nDuVTqobD4b8mGGyPMbIZnqyMsEcaGQy67XIw/Jw==";
            const string databaseId = "Test";
            const string documentCollectionId = "Test";
            const int documentCount = 500;

            var client = new DocumentClient(new Uri(serviceEndpoint), accountKey);

            await client.CreateDatabaseIfNotExistsAsync(new Database { Id = databaseId });
            Console.WriteLine($"Created database {databaseId}");
            await CreateDocumentCollectionAsync(client, databaseId, documentCollectionId);

            var (readElapsed1, upsertElapsed1) = await ReadOrCreateDocumentsAsync(client, databaseId, documentCollectionId, documentCount);
            Console.WriteLine($"Empty collection: read = {readElapsed1}, upsert = {upsertElapsed1}");
            var (readElapsed2, upsertElapsed2) = await ReadOrCreateDocumentsAsync(client, databaseId, documentCollectionId, documentCount);
            Console.WriteLine($"Non-empty collection: read = {readElapsed2}, upsert = {upsertElapsed2}");

            await client.DeleteDatabaseAsync(UriFactory.CreateDatabaseUri(databaseId));
            Console.WriteLine($"Deleted database {databaseId}");

            Console.ReadKey();
        }

        private static async Task CreateDocumentCollectionAsync(DocumentClient client, string databaseId, string documentCollectionId)
        {
            try
            {
                var documentCollectionUri = UriFactory.CreateDocumentCollectionUri(databaseId, documentCollectionId);
                await client.ReadDocumentCollectionAsync(documentCollectionUri);
                await client.DeleteDocumentCollectionAsync(documentCollectionUri);
                Console.WriteLine($"Deleted document collection {documentCollectionId}");
            }
            catch (DocumentClientException exception)
            {
                if (exception.StatusCode != HttpStatusCode.NotFound)
                    throw;
            }

            await client.CreateDocumentCollectionAsync(
                UriFactory.CreateDatabaseUri(databaseId),
                new DocumentCollection { Id = documentCollectionId },
                new RequestOptions { OfferThroughput = 10000 }
            );
            Console.WriteLine($"Created document collection {documentCollectionId}");
        }

        private static async Task<(TimeSpan ReadElapsed, TimeSpan UpsertElapsed)> ReadOrCreateDocumentsAsync(DocumentClient client, string databaseId, string documentCollectionId, int count)
        {
            var readElapsedTicks = 0L;
            var upsertElapsedTicks = 0L;

            for (var i = 0; i < count; i += 1)
            {
                var documentId = i.ToString();
                var readStopwatch = Stopwatch.StartNew();
                await ReadDocumentAsync(client, databaseId, documentCollectionId, documentId);
                readElapsedTicks += readStopwatch.ElapsedTicks;
                var createStopwatch = Stopwatch.StartNew();
                await UpsertDocumentAsync(client, databaseId, documentCollectionId, documentId);
                upsertElapsedTicks += createStopwatch.ElapsedTicks;

                if (i % 100 == 99)
                    Console.WriteLine($"Processed {i + 1} documents");
            }

            return (new TimeSpan(readElapsedTicks), new TimeSpan(upsertElapsedTicks));
        }

        private static async Task<Document> ReadDocumentAsync(DocumentClient client, string databaseId, string documentCollectionId, string documentId)
        {
            var documentUri = UriFactory.CreateDocumentUri(databaseId, documentCollectionId, documentId);
            try
            {
                var response = await client.ReadDocumentAsync(documentUri);
                return response.Resource;
            }
            catch (DocumentClientException exception)
            {
                if (exception.StatusCode != HttpStatusCode.NotFound)
                    throw;
                return null;
            }
        }

        private static Task UpsertDocumentAsync(DocumentClient client, string databaseId, string documentCollectionId, string documentId)
        {
            var documentCollectionUri = UriFactory.CreateDocumentCollectionUri(databaseId, documentCollectionId);
            var document = new Document
            {
                Id = documentId
            };
            return client.UpsertDocumentAsync(documentCollectionUri, document);
        }
    }
}