HubSpot/HubL spacing style field breaking require_css & scope_css

Question

I am encountering a strange issue with a small snippet of HubL code, I've added a 'spacing' field to my fields.json file as below:

    {
        "label": "Margin",
        "name": "mobile_margin",
        "type": "spacing",
        "visibility": {
            "hidden_subfields": {
                "padding" : true
            }
        }
    }

And I am referencing said field in my code using what works for it's sibling field (related to padding):

    {% require_css %}
        <style>
            {% scope_css %}

                .......

                {% if module.styles.container_styles.mobile.mobile_padding_margin.mobile_margin %}
                    {{ module.styles.container_styles.mobile.mobile_padding_margin.mobile_margin.css }};
                {% endif %}

                .......

            {% end_scope_css %}
        </style>
    {% end_require_css %}

However the inclusion of this small snippet in fact stops the rendering of the entire <style> block, I presume due to some inability to compute what should be rendered by this snippet.

After some head bashing I decided to pprint the field to check it's definitely populated, and as you can see below, this is what is returned:

    {{ module.styles.container_styles.mobile.mobile_padding_margin.mobile_margin.css | pprint }}
    {# Return: (String: margin-top: 16px; margin-bottom: 21px; ) #}

I am baffled as to why it won't render the style, and any help would be appreciated. I know there is the HubSpot support, but it's extremely slow and find the Stackoverflow community much more punctual and helpful in their responses.