I am running Magento 2.1.5, created a test product, assigned them in a category, then deleted them in the catalog, but the item still listed in the category under "products in category", Why?
I think I know why... the item was created as configurable product, when created, the system automatically created a bunch simple products along with the configurable products. I assumed if I removed the configurable product it will also remove all the simple products that itself had created. How strange the way it set up this way... why? anyway, I had to go in to product/catalog and delete all those simple products manually.