Variable's value is increasing incorrectly

Hi, I've tried to make an exp system.
So I made a number, player persistent variable that stands as exp. When an entity is killed by a player (in that case, Pokemon, cause I'm making it with pixelmon mod) it drops a placeholder item that when "in inventory tick" should be instantly removed from the player in order to add +5 to exp variable according to its procedure. But the problem is that, variable changes are very strange. Sometimes, it works and I get normally 5 exp, but sometimes I get more than that, for example, 6 or 7. I wonder if it has something to do with the "inventory tick" calculation.

Item procedure trigger:

Procedure: