More details here:
https://github.com/dotnet/corefx/issues/17330#issuecomment-288078562

In summary, some clients (e.g. libcurl) stop sending request content if they concurrently receive an error status code in response from the server. If an app on kestrel ignores the request data and immediately sends a response with an error status, the client may as such stop sending the request data, which in turn causes kestrel to fail with a BadHttpRequestException, but it doesn't complete the chunked encoding response by sending a terminating 0-length chunk, nor does it close the connection. As a result, the client is left waiting indefinitely for the remainder of the response that never comes, and effectively deadlocks until timeout.