In fact, the StreamingTimeoutMillis property is available in the .NET client library, while no equivalent setting was made available in the HTML client library.

Note that, in web applications, the stream-sense timeout may also expire because of slow processing in the page startup phase and this can be avoided by placing the changeStatus("STREAMING") request later in the initialization process.

However, we see that you had to increase the limit also in a .NET client.
Which timeout value did you have to use?
Do you know the details of the client environment? If you do, could you figure out why a streaming request should take more than 5 seconds to succeed?