A couple of the Forbidden Reach rares don't trigger an alert until you mouse over the NPC/are in range for the nameplate to be visible.
So far I've noticed this behavior on the following rares: Volcanakk, Wyrmslayer Angvardi, Lady Shaz'ra and Pyrachniss.

Tell me if you need any more info and I'll happily gather it for you while playing.

For me all these rares are working fine. Never missed a single alert.