Why aren't you just giving the ability to the item directly? That will ALWAYS work, it just needs to be an item ability. Also, a few notes about Item abilities.
If you have multiple abilities on one item, you can only have one that is actively used. (E.G. An ability that you click to use)
Let's say you have a Kelen's Dagger of Escape but add a 5+ all stats ability to it. MAKE SURE your actively used ability is above the passive on in the Abilities section of the item. If it isn't the cooldown on the item won't show up. (The art that shows you how much cooldown is left on the item)
If you have an item that has an actively used ability, make sure the "actively used" box is checked. Also make sure it's unchecked if you have passive abilities on it.