I have the same issue.. Actually it is not working at all.
Strange thing is I was using https://github.com/StefH/McpDotNet.Extensions.SemanticKernel

await _kernel.Plugins.AddMcpFunctionsFromSseServerAsync("McpServer", new Uri(url), httpClient: _httpClient);

And that worked fine. I wanted to switch to the native SK code but now it does not work anymore.