Some NPC names like Chromie in Orgrimmar or Thrall, Liadrin, Khadgar in the example below don't show up. They do showup if KUI is disabled so it isn't my blizzard settings. I have always show friendly namepates on and as can be seen by the fact that other npc names show up I also have that on too.

Same issue here, can't find a reason why it happens, seem to affect random targets (players and friendly NPCs only), started about a week ago.

@Budpop found the culprit - its the Target Helper addon, at least for me, and specifically this setting. It seems to not know what to do with elite friendly nameplates, tries to apply border, and instead just does not show anything.