So I took a look at your code, and your item is being rendered, just with no width so you can’t see it. By adding width: dimensions.fullWidth to your top level View on the MyListItem, it fixes this issue.
your separator item has a width on it. for one item, there is no separator item rendered, but for more than one, there is. So once a separator item was rendered, it would stretch the flatlist to the width of that separator item.