Hi,
It's a shame you didn't provide a screenshot of the settings of the product.
I can only suppose that the product for which you provided a link isn't in either categories you specified in the custom field.
I suppose that it might be in a sub category of these categories, but you didn't activate the "include sub categories" setting of the custom field and thus the custom field is skipped.
Besides that, it could potentially be a template issue as you hinted at. To check on that, simply switch temporarily to the default template of Joomla and look at that same page. If the field is displaying with the default template and not your template, it's indeed a view override issue in your template. Otherwise, it's caused by something else.