I would believe diplomats would be somewhat resistant against mass delusion, considering their selection (and possibly training).
Mass delusion has also been one of the leading hypothesis from the very first story on this phenomenon. Being aware of the concept would tend to dispel it, which apparently did not happen.
I'm sure those with more information have considered that possibility. The ongoing investigation leads me to believe they are not quite as sure of it as the HN crowd is. Maybe some of the cases appeared independently?
Mass delusion has also been one of the leading hypothesis from the very first story on this phenomenon. Being aware of the concept would tend to dispel it, which apparently did not happen.
I'm sure those with more information have considered that possibility. The ongoing investigation leads me to believe they are not quite as sure of it as the HN crowd is. Maybe some of the cases appeared independently?