Alright, i just made an simple trigger that does basically the exact thing yours does, just without the random chance. Honestly, the only thing that i changed from my trigger to yours, is that i dont have 2 conditions that are of the same thing..here is my trigger.
Ignoring the unit is attacked (this is just so i don't have to make another trigger for a random chance), you can see that its basically exactly the same (well, without a full floating text part). The only thing i did different, was that i made another trigger that when a unit picks up the item, he was put into a unit group, and my condition checks if the unit is in the group or not.
So, your problem is probably something wrong with either the condition, or more likely the trigger that calls that one. Since im using a event that happens every time, there is no need to make a separate trigger to call it, however your trigger doesn't have a event, meaning that it has to be called in a separate trigger. If something is wrong with the trigger that is supposed to call it, it wont work.
If its not a problem with the condition, or the other trigger, then i honestly dont have a clue whats wrong, unless your simply very, very unlucky and not getting the random chance at all..but thats unlikely.