https://www.curseforge.com/wow/addons/tidy-plates-threat-plates/issues/567

The yellow star elite icon doesn't show on some nameplates, it started recently. A pack of 4 elites in a dungeon and maybe 1 or 2 won't have the star on occasion. Not sure why it's happening but I'll post more details if I find anything.

I thought maybe it was just mobs that spawn infront of you, which it does appear to be a lot more comon with that but also sometimes they spawn infront just fine with some showing as elite and some not.

Examples from Violet Hold