Sometimes these items dont proc to execute minions and give gold/health. Did a search on this and didnt find anything regarding it, surprisingly. And this is while playing Alistar, which isnt a ranged attack.
Id be willing to bet you were out of charges. Look for rotating orbs on your character. The more you upgrade the item, the more orbs you will see.
Pretty sure I have charges on the items when I go to execute the minions. I look at the icon to see how many charges I have before I go to execute. I've noticed this has happened with Kalista in lane, maybe that was it.
