Why Are My Microsoft Graph Calls to SharePoint Unreliable in ASP.NET Core API?

Question

I'm currently developing an ASP.NET Core API that interacts with SharePoint via Microsoft Graph. While the setup works occasionally, I'm experiencing significant reliability issues. The API calls to Graph work about 50% of the time and fail the rest of the time without any changes to the code or environment.

Setup:

Custom Authentication Provider:

public class CustomAuthenticationProvider : IAuthenticationProvider
public CustomAuthenticationProvider(ITokenAcquisition tokenAcquisition)
{
    _tokenAcquisition = tokenAcquisition;
}

	public async Task AuthenticateRequestAsync(HttpRequestMessage request)
	{
	    string[] scopes = new[] { "https://graph.microsoft.com/.default" };
	    string accessToken = await _tokenAcquisition.GetAccessTokenForUserAsync(scopes);
	
	    request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", accessToken);
	}
}

Graph Service Client Initliaziation:

#### Sample Graph Query:


```csharp
var query = $"fields/Number '{itemId}'"; 
var page = await _graphServiceClient.Sites[siteId].Lists[listId].Items
    .Request()
    .Expand("fields")
    .Filter(query)
    .GetAsync();

Problem

The API works sporadically, failing immediately with errors like:

• "An existing connection was forcibly closed by the remote host."
• MSAL Debug Info:
  • "False MSAL 4.61.3.0 MSAL.NetCore .NET 8.0.11 Microsoft Windows 10.0.22631 [2024-12-11 09:13:35Z] Only in-memory caching is used. The cache is not persisted and will be lost if the machine is restarted"

The issue occurs regardless of the size of the SharePoint library:

• Libraries with 10,000–15,000 documents fail.
• Libraries with just 2 documents also fail.

Observations

• This does not seem like throttling, as the returned error codes don't match those documented for throttling scenarios.
• The failures suggest an intermittent connectivity issue, almost as if there's no internet.

Environment

• NuGet Packages:
  • Microsoft.Graph v4.54.0
• Dotnet Version:
  • 8.0.404
• OS:
  • Microsoft Windows 10.0.22631

What I Need Help With

1. Diagnosing the root cause: Could this be related to network issues, MSAL caching, or something else entirely?
2. Resolving intermittent connectivity: Any tips for improving reliability when making Graph API calls?
3. Error interpretation: What does the error "An existing connection was forcibly closed by the remote host" suggest in this context?