Stateful connection is intermittent.

Describe the bug
Without o.SessionMode = HttpServerSessionMode.Stateless; or with the line commented out, the connection sometimes succeed and sometimes failed. I don't believe this should cause the connection to fail at all since otherwise, the product won't be able to support the stateful connection as claimed in https://github.com/modelcontextprotocol/csharp-sdk/blob/main/docs/concepts/transports/transports.md#streamable-http-server-aspnet-core

Set SessionMode = HttpServerSessionMode.Stateful explicitly when your server needs stateful sessions for unsolicited notifications, resource subscriptions, or per-client isolation.

and therefore, it is a BUG.

To Reproduce
Steps to reproduce the behavior:

1. Create a streaming HTTP MCP server and deploy to a k8s cluster. Local cluster is fine.
2. The server should be created without o.SessionMode = HttpServerSessionMode.Stateless;. So it is a stateful connection.
3. Try to connect to the service either from Postman MCP client OR npx @modelcontextprotocol/inspector

Expected behavior
Successful connection 100%

Logs
If applicable, add logs to help explain your problem.

Additional context
Add any other context about the problem here.

Read docs/concepts/transports/transports.md at the Streamable HTTP server section, then reproduce the stateful setup in a local Kubernetes cluster using Postman MCP or @modelcontextprotocol/inspector. Compare behavior with and without HttpServerSessionMode.Stateless; done means the stateful server connects successfully and consistently.