Temp and power draw inconsistency

I have a ROG Phone 8 pro and recently started to play LoL:WR but everytime I open the app and play a game it's stable at 39c and bypass charging can't sustain the load given by the game, only after closing the game and reopening it 1-2 times and playing a game bypass charging works fine again and the game is stable at 34c. any idea as to why this happens and possibly a solution to this?