Need help with gambling vendor

Does anyone know how this vendor works? It says it gains charges for killing unique monsters. So I go kill the giant gorilla in jungle and get a charge. The item sucks so I need another. I go kill him again and get nothing. So I go kill Witch boss in the bog instead and still didn't get a charge. Is there a time limit on getting charges or something?

I am not sure if you can repeat farm the same mob for counters during campaing, never tried, did you reset the zone properly via the map? teleport out of the map, ctrl-click your target zone select new instance.
If you get to Endgame, Alva does not have a counter anymore.

Yes I did a new zone, or else the giant gorilla wouldn't have been up again.