Ok, fooling around with the idea of dual wielding dagger Warlock (assuming pact of the blade becomes a thing, short sword+dagger) when I noticed Hex did not proc from the offhand attack.
The description in the dnd 5e PHB says Hex “deals an extra 1d6 necrotic damage to the target whenever you hit it with an attack”
The sticking point could be that it's a bonus action, but I would say that's still an attack. In addition, it clearly is not a once per turn proc, currently it procs 3 times off scorching ray (A MUST HAVE for fiend Warlocks).
So my question is, is it working as intended?