Lucian Bug in 5.23

Played a ranked game as Lucian . At level 6 i used my ult to clear a minion wave, but it didnt clear the wave... it killed ONE minion. The minion was able to live through the entire ult.. and took VERY VERY little damage. its supposed to be 400% dmg to minions... seemed like -400%.. bug?

rito pls