While it is not mentioned on the event page, there seems to be some confusion as to wether the 5 minute minimum time in battle requirement is in effect or not. If you are leaving games before this point and getting wins, then they might not be counting because of this.
I am unsure if the timer is present or not, I generally stay to atleast 5 minutes away due to premium, but if you do not then perhaps this is the issue. Ask for time to premium in battle and see if wins earned after the 5 minute marker start to count towards the objectives.