What were you expecting to happen, and what actually happened
Upgraded Gong from common to uncommon while having 0 tokens left (not sure if that matters), but in doing so he did not give an extra token on the day of the upgrade.
What I was expecting to happen is he would give 1 token battle for all 3 pvp modes the day of his upgrade.
How often does this happen? When did it begin happening?
Once, likely every time though.
Steps to make it happen again
1: Upgrade Gong a rarity.
2: Have some of pvp at full battles and not full battles to see if it interacts differently (all 3 of mine were at 0 battles, so not sure how it works on unused full capacity battles or just not on 0s).