It just sometimes returns the following even when the kit has data, this happens after you have edited or updated the kit or created one but has some styles.
It was for a simple reason of Kit's post content is blank, in which Elementor considers it invalid. I've added Analog\Elementor\Kit\Manager\get_kit_content() to be used when creating a kit that fixes the issues.
It just sometimes returns the following even when the kit has data, this happens after you have edited or updated the kit or created one but has some styles.