Just added 5 level 0 cards with versatile (no firearms) and these deck error "Contains forbidden cards (cards not permitted by Investigator)" is shown:
Versatile makes you take 5 extra cards but only 1 card can be outside of your normal deckbuilding rules. Looks like this deck added multiple non guardian/mystic cards.
I don't know if I am missing something.
Just added 5 level 0 cards with versatile (no firearms) and these deck error "Contains forbidden cards (cards not permitted by Investigator)" is shown:
Before the update: https://arkhamdb.com/deck/view/3564325
After the update: https://arkhamdb.com/deck/view/3578557
Maybe I give a wrong interpretation to the Versatile text?