The stealth detection indicator is being hidden by the unit frames, i've noticed this in the atal'dazar dungeon. The indicator is behind the unit frame and visible just below and above the unit frame, though not obvious.

Can't fix this directly, it's a blizzard issue.

You can vertically move nameplate frames slightly by changing frame_vertical_offset: /knp set frame_vertical_offset 10. You can change 10 to anything else, however this will only move KNP's graphical representation of nameplates. Not the clickbox; the clickbox can't be moved by addons.