Multiselect custom attribute module is not showing on layered navigation but shows on product edit

[marcintota03e5]

I'm getting a little frustrated with this, below is code i have to create a custom multi-select attribute for a product, it uses a custom source to pull the data for it from a database table, when selecting the attributes on the product edit screen it saves the id values (primary keys of the table the data comes from).

I thought that the source would also be used on the front end to create check boxes, but nothing i do makes it show up (and i have added a multi select in the admin directly and that attribute shows up just fine):

$eavSetup->addAttribute(
    Product::ENTITY,
    'svgs',
    [
        'type' => 'varchar',
        'label' => 'Select SVG/Filters',
        'input' => 'multiselect',
        'source' => 'Vendor\Module\Model\Config\Attributes\SvgOptions',
        'backend'=> 'Magento\Eav\Model\Entity\Attribute\Backend\ArrayBackend',
        'required' => false,
        'sort_order' => 100,
        'global' => ScopedAttributeInterface::SCOPE_STORE,
        'group' => 'Product Overview SVG/Filters',
        'visible_on_front' => true,
        'used_in_product_listing' => true,
        'filterable'=>true,
        'searchable'=>true,
        'comparable'=>false,
        'user_defined'=>true,
        'apply_to' => 'simple,configurable,virtual,bundle,downloadable',
        'is_used_in_grid' => true,
        'is_visible_in_grid' => false,
        'is_filterable_in_grid' => true
    ]
);

 My data source is this:

public function getAllOptions() : array
{

    /** @var Collection $svgCollection */
    $svgCollection = $this->svgCollectionFactory->create();

    /** @var Collection $svgCategoryCollection */
    $svgCategoryCollection = $this->svgCategoryCollectionFactory->create();

    // get all categories
    $categories = $svgCategoryCollection->setOrder('name','ASC');

    // for each category as an option group, assign SVGs
    $options = [];

    /** @var Category $category */
    foreach($categories as $category) {

        // reset where in collection so each loop works
        $svgCollection->clear()->getSelect()->reset('where');

        // get svgs in this category
        $svgs = $svgCollection->addFieldToFilter('category_id',$category->getId())
            ->setOrder('display_name','ASC');

        if($svgs->count() > 0){

            // create svgs array
            $svgOptions = [];
            /** @var SVG $svg */
            foreach ($svgs as $svg) {
                $svgOptions[] = [
                    'label'=>$svg->getData('display_name'),
                    'value'=>$svg->getId()
                ];
            }


            // add category with svgs to options
            $options[] = [
                'label'=>$category->getData('name'),
                'value'=>$svgOptions
            ];
        }
    }


    return $options;
}

All the options show in the admin and save no problem, it's just the layered nav they won't show up on