Since a change was made this season that you could only complete vanguard bounties in the vanguard playlist it's now terrible to get enemy specific bounties. You have to be extremely lucky and hope the vanguard playlist loads a strike that has that specific enemy type otherwise you have to depart and try again. Sometimes you get like 3 of these enemy specific which take up all your bounty space and you might load into a strike which has none of that enemy type.