Reading my background, I have pass most of the last year at Elk River with my uncle, which is something Venial do when he need to relax or keep very low profile. For short period of time, he wouldn't bother to carry his things, but for as he seems to have spend a lot of time, he would surely have brought it to his uncle place, so he could have worked on restocking his own supplies.
As he exected the last mission to be longer, he would have prepare the chest before leaving and would have asked to bring it later. That is why he hadn't the chest with him when he arrived at Devil's Hand.
So, his chest is in Elk River, but someone there is waiting for a message from him to bring it to bring is at Devil's Hand, or elsewhere if needed I would tell.