Add properties to CatalogContent (again)

I am trying to add a property to my own CatalogContent.

Previous this topic was created: Add properties to CatalogContent | Optimizely Developer Community And was closed with "Not working".

Then I saw this blog post which says it can be done: https://stefanolsen.com/posts/catalog-roots-can-finally-be-customized-in-optimizely-commerce/ 

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I can see my new property in the UI, and when the UI is reentered, I can still see the value I set. But I cannot read the value using code. I am trying to load the properties with something like this:

int catalogId = -2147483645;
_contentLoader.Get<MyCatalogContent>(_referenceConverter.GetContentLink(catalogId, CatalogContentType.Catalog, -1))

and 

var catalog = _contentLoader.GetAncestors(product.ContentLink)
	.OfType<MyCatalogContent>()
	.FirstOrDefault();
var x = catalog.MyProperty; // null

I can see the built in values, but not my own.

Any ideas how to read the value for my custom property?