NPCScan not alerting

I put the NPCScan addon on, cleared the cache, and all that good stuff. But for some reason it still doesn't alert when a rare that's on the list shows up.

For example: I was questing in Terrokar Forest and when I had to hearth back for something then port back to Shattrath, the npcscan cache says "Crippler" was cached. This isn't a pet that it could randomly cache while in a city, it's an undead npc. One that obviously popped up while I was questing in that area, but the addon didn't go off! Same thing happened before with Speaker Mar'grom in Blade's Edge Mountains. Thankfully at least that one I was able to go back and look and sure enough he was there. But again, the add on didn't alert me, and I was standing right in front of him!

Has anyone else had this problem? And what would the solution be?