Product is missing when choosing sort by latest on the product list widget?

It is based on the date when the product was available on the webshop for the first time. 

The Latest products option in the Sort by selection is based on the date the product was first made available on the webshop. If a product was unpublished and then republished, it won’t change its position in the "Latest products" sorting.

Newly added products will appear in the Latest products sort after the product list updates, wich is in general every 20 minutes.