RateLimit headers are not returned by SharePoint online

Target SharePoint environment

SharePoint Online

What SharePoint development model, framework, SDK or API is this about?

SharePoint CSOM

Developer environment

Windows

What browser(s) / client(s) have you tested

• 💥 Internet Explorer
• 💥 Microsoft Edge
• 💥 Google Chrome
• 💥 FireFox
• 💥 Safari
• mobile (iOS/iPadOS)
• mobile (Android)
• not applicable
• other (enter in the "Additional environment details" area below)

Additional environment details

• Microsoft.SharePointOnline.CSOM 16.1.25110.12000
• .NET framework 4.8

Describe the bug / error

We have an RateLimit implementation based on this example on GitHub: https://github.com/OneDrive/samples/blob/master/scenarios/throttling-ratelimit-handling/readme.md

In a development environment we get RateLimit headers returned from SharePoint, but with ClientIDs from a few customers we almost never get RateLimit headers returned.

Instead the customer app is throttled with 429 Too Many Requests errors with retry times of sometimes even 200+ seconds.

In Fiddler the network traffic is clearly visible that there are no RateLimit headers.

In the production environment there are around 4 processes which run with the same clientid which do background processes (Windows agents), and 4 processes (websites) which serve user requests. The websites processes run under a different clientid, but this does not make a difference. All processes are affected with many 429 errors.

In which case does SharePoint online give not first RateLimit headers, but returns 429 errors?

Steps to reproduce

1. Use the example on GitHub https://github.com/OneDrive/samples/blob/master/scenarios/throttling-ratelimit-handling/readme.md
2. Change the function SharePointCSOMCallAsync

private async Task SharePointCSOMCallAsync(Microsoft.SharePoint.Client.ClientContext clientContext)
{
	var site = clientContext.Site;
	var rootWeb = site.RootWeb;
	var contentTypes = rootWeb.ContentTypes;
	var currentUser = rootWeb.CurrentUser;
	var fields = rootWeb.Fields;

	clientContext.Load(site, s => s.Url, s => s.ServerRelativeUrl);

	clientContext.Load(rootWeb, r => r.Id, r => r.Description, r => r.Title, r => r.Url);
	clientContext.Load(rootWeb, r => r.Language, r => r.ServerRelativeUrl);

	clientContext.Load(currentUser, u => u.IsSiteAdmin, u => u.LoginName);

	clientContext.Load(contentTypes, c => c.Include(ctt => ctt.Fields.Include(f => f.InternalName), cct => cct.FieldLinks.Include(fl => fl.Name), ctt => ctt.Name, ctt => ctt.Group));
	clientContext.Load(fields, fi => fi.Include(f => f.InternalName, f => f.Id, f => f.Group, f => f.Hidden, f => f.ReadOnlyField, f => f.Title, f => f.CanBeDeleted));

	clientContext.Load(rootWeb, r => r.RoleDefinitions.Where(rd => !(rd.RoleTypeKind == RoleType.Guest || rd.RoleTypeKind == RoleType.RestrictedGuest)).Include(rd => rd.Id, rd => rd.Name, rd => rd.BasePermissions, rd => rd.RoleTypeKind));
	clientContext.Load(rootWeb, r => r.RoleAssignments.Include(ra => ra.Member.LoginName, ra => ra.Member.PrincipalType, ra => ra.Member.Id, ra => ra.RoleDefinitionBindings.Include(rdb => rdb.Id, rdb => rdb.RoleTypeKind, rdb => rdb.Name)));

	var siteUsers = site.RootWeb.SiteUsers;
	site.RootWeb.Context.Load(siteUsers, us => us.Include(u => u.Title, u => u.LoginName, u => u.PrincipalType, u => u.Email, u => u.Id));
	loadDefaultTitleDescriptionResource(clientContext.Site.RootWeb);
	await clientContext.ExecuteQueryAsync();
	Console.WriteLine(site.RootWeb.Title);

	IncrementCallsDone();

}

private static void loadDefaultTitleDescriptionResource(Microsoft.SharePoint.Client.Web web)
{
	var cultureNameEN = "en-US";
	var cultureNameNL = "nl-NL";
	_ = web.TitleResource.GetValueForUICulture(cultureNameEN);
	_ = web.TitleResource.GetValueForUICulture(cultureNameNL);
	_ = web.DescriptionResource.GetValueForUICulture(cultureNameEN);
	_ = web.DescriptionResource.GetValueForUICulture(cultureNameNL);
}

4. Comment method 'SharePointRestCallAsync' and 'GraphRestCallAsync', so only method 'SharePointCSOMCallAsync' is called.

// Test a SharePoint Rest call
// await SharePointRestCallAsync(client, sharePointAccessToken);

// Test a Graph Rest call
//await GraphRestCallAsync(client, graphAccessToken);

// Test a CSOM call
await SharePointCSOMCallAsync(clientContext);

5. Configure the app (for instance with 5 threads)
6. Start Fiddler (or any other app which can show network traffic)
7. Run the app

Expected behavior

In the development environment we get RateLimit headers.