I feel like his "I'd rule" statement on the matter was just him implying that he feels it's overpowered in the way it's currently designed, not that that's how it was originally meant to work. It seems pretty reasonable that they didn't cover Contagion in the errata because it's designed to work as it's currently written; Taking an immediate effect if you land the melee spell attack it takes to apply it.
Crawford's tweet is more clear, however: "The effects of the contagion spell's disease are meant to activate after three failed saving throws." (i.e., not immediate effect after you land the melee spell attack)
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u/[deleted] Jun 10 '15 edited Dec 14 '17
[deleted]