In the Visual Editor I have created a new row and then added the Content promotion products column. If I then select only variants, nothing is outputted and the promo feed comes back empty. If I select the master product as well, I do see the variants, but also the master. In the site I am using this we only show variants, so showing the master also is not an option. I reproduced this on a clean Rapido solution. When I look into the index with Luke, the ProductIdVariantCombination seems to have the correct value: the product ID and variant ID separated by a space.
This results in no products:
And this results in the display of the master and the two variants:
Am I missing something? Or is this a bug?