I have only been able to get it to proc once with single handed versus a teammate. It has never triggered during combat. This thread (https://forums.obsidian.net/topic/84499-vent-pick/?hl=%2Bvent+%2Bpick) talked about it as well but I don't know if they filed a bug report so here it is. 

Heya nem0!

 

Vent Pick was set up in a way that made it only possible to proc once. After this initial proc, it would be unable to ever utilize the Flames of Devotion ability again. This has been fixed in our internal build, and you should see the change reflected in the next patch =)

 

Thanks!