The addon doesn't seem to detect NPCs by Nameplates. For example world bosses in Pandaria are only detected by mouseover, so before I alt tab out of the game I have to make sure that cursor is positioned correctly. I'm using ElvUI's nameplates if it matters.

It normally does work for me. I'll go verify somewhere -- I might not have done a full "wait for a spawn and see if that triggers it" in a while, so the timing might have gone messy.