Report about champion pi decreasing

Siva22ak

I don't know why it's happening every time I rank up my 6* champion rank 2 to 3 their pi decreasing why it's happening

Crcrcrc

It’s due to challenger rating, a hidden stat that influences crit damage, power gain from hits, etc. It drops a few points from the rankup but balances out and increases by the time they’re max level