Phenocryst is immune to charm?

[not alla]

Phenocryst is lvl 58 and should be charmable with Dictate. I remember on live it was an enchanter 'freebie' as the faction to finish the quest only required being charmed by Dictate for turn-in.

Is there a specific reason by it would be triggered as 'charm immune' it's not a specifically resistant mob and it's lvl 58, it falls directly into the wheelhouse for Dictate.