Disabling that setting should take care of the issue with requests being made to /wp-json/wp-discourse/v1/discourse-comments. Let me know if it doesn’t.
I’m unsure why requests to that route were being sent with the post_id=undefined parameter. The request should be using the id of the current post. If the post_id parameter is set to undefined then the function that handles that route will return an empty string. Enabling the Load Comments With Ajax option will result in more requests being made to your server than if the option is not enabled, so unless you are running into issues with comments not being updated due to caching, it is best to leave that option disabled.