I am having difficulty tracking down the cause of this exception.

Calling Code

// reduced for brevity
endpoints.MapGet("/sse/workorder", async Task (HttpContext context, CancellationToken token) => {
    while (!token.IsCancellationRequested)
    {
        await context.SSESendEventAsync(new SSEEvent(), token);
        await Task.Delay(TimeSpan.FromSeconds(2), token);
    }
}

public static async Task SSESendEventAsync(this HttpContext ctx, SSEEvent e, CancellationToken token)
{
    ArgumentNullException.ThrowIfNull(ctx);
    ArgumentNullException.ThrowIfNull(e);

    if (!string.IsNullOrWhiteSpace(e.Id))
    {
        await ctx.Response.WriteAsync($"id: {e.Id}n", token);   // <-exception occurs here.
    }
    ...
}

Also, if pertinent, this continually runs asynchronously elsewhere in the program…

try
{
    while (!token.IsCancellationRequested)
    {
        await ctx.Response.WriteAsync(": nn", token);

        await Task.Delay(TimeSpan.FromSeconds(10), token);
    }
}
catch (Exception ex) when (ex is OperationCanceledException) { }

The Exception

15:48:40:643    Exception thrown: 'System.ArgumentNullException' in System.Private.CoreLib.dll
15:48:40:643    Exception thrown: 'System.ArgumentNullException' in System.Private.CoreLib.dll
15:48:40:643    Microsoft.AspNetCore.Routing.EndpointMiddleware: Information: Executed endpoint 'HTTP: GET /sse/workorder'
15:48:40:643    Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware: Error: An unhandled exception has occurred while executing the request.
15:48:40:643    
15:48:40:643    System.ArgumentNullException: Value cannot be null. (Parameter 'array')
15:48:40:643       at System.Buffers.SharedArrayPool`1.Return(T[] array, Boolean clearArray)
15:48:40:643       at System.IO.Pipelines.StreamPipeWriter.FlushAsyncInternal(Boolean writeToStream, ReadOnlyMemory`1 data, CancellationToken cancellationToken)
15:48:40:643       at System.Runtime.CompilerServices.PoolingAsyncValueTaskMethodBuilder`1.StateMachineBox`1.System.Threading.Tasks.Sources.IValueTaskSource<TResult>.GetResult(Int16 token)
15:48:40:643       at System.Threading.Tasks.ValueTask`1.GetTaskForValueTaskSource(IValueTaskSource`1 t)
15:48:40:643    --- End of stack trace from previous location ---
15:48:40:643       at SSE.SSEHttpContextExtensions.SSESendEventAsync(HttpContext ctx, SSEEvent e, CancellationToken token) in C:[redacted]SSEHttpContextExtensions.cs:line 50
15:48:40:643       at SSE.Startup.<>c__DisplayClass3_0.<<Configure>b__5>d.MoveNext() in C:[redacted]Startup.cs:line 529
15:48:40:643    --- End of stack trace from previous location ---
15:48:40:643       at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|7_0(Endpoint endpoint, Task requestTask, ILogger logger)
15:48:40:643       at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddlewareImpl.Invoke(HttpContext context)
15:48:40:643    Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware: Warning: The response has already started, the error page middleware will not be executed.
15:48:40:643    Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware: Error: An unhandled exception has occurred while executing the request.
15:48:40:643    
15:48:40:643    System.ArgumentNullException: Value cannot be null. (Parameter 'array')
15:48:40:643       at System.Buffers.SharedArrayPool`1.Return(T[] array, Boolean clearArray)
15:48:40:643       at System.IO.Pipelines.StreamPipeWriter.FlushAsyncInternal(Boolean writeToStream, ReadOnlyMemory`1 data, CancellationToken cancellationToken)
15:48:40:643       at System.Runtime.CompilerServices.PoolingAsyncValueTaskMethodBuilder`1.StateMachineBox`1.System.Threading.Tasks.Sources.IValueTaskSource<TResult>.GetResult(Int16 token)
15:48:40:643       at System.Threading.Tasks.ValueTask`1.GetTaskForValueTaskSource(IValueTaskSource`1 t)
15:48:40:643    --- End of stack trace from previous location ---
15:48:40:643       at SSE.SSEHttpContextExtensions.SSESendEventAsync(HttpContext ctx, SSEEvent e, CancellationToken token) in C:[redacted]SSEHttpContextExtensions.cs:line 50
15:48:40:643       at SSE.Startup.<>c__DisplayClass3_0.<<Configure>b__5>d.MoveNext() in C:[redacted]Startup.cs:line 529
15:48:40:643    --- End of stack trace from previous location ---
15:48:40:643       at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|7_0(Endpoint endpoint, Task requestTask, ILogger logger)
15:48:40:643       at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddlewareImpl.Invoke(HttpContext context)
15:48:40:643       at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddlewareImpl.Invoke(HttpContext context)
15:48:40:643       at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
15:48:40:643       at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
15:48:40:643       at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddlewareImpl.Invoke(HttpContext context)
15:48:40:643    Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware: Warning: The response has already started, the error page middleware will not be executed.
15:48:40:643    Microsoft.AspNetCore.Server.IIS.Core.IISHttpServer: Error: Connection ID "18158513719837982798", Request ID "40000052-0005-fc00-b63f-84710c7967bb": An unhandled exception was thrown by the application.

This exception (along with ArgumentOutOfRangeException) occurs intermittently and infrequently here. Sometimes days, sometimes minutes.

I would appreciate any help in finding the root cause, or any tips on how to investigate it further.