As of Grosh 3.4, the system analyses the product name you type in to understand what you're actually entering. Unlike other grocery shopping apps, Grosh tries to understand what you add to your list in order to generate relevant suggestions. So "2kg potatoes" is the same grocery as "potatoes", so therefore we do not treat 2kg as part of the grocery name, but what we call variant information.
If you're entering variant information but it does not get shown on the shopping list, it might be because you've turned off using variant information for the list. Tap select list, then the edit icon to the right of the list name to show list properties. Under list properties ensure "Use variant info" is toggled on.