Garen's Q wont attack the nexus

I have been experiencing a problem with Garen's Decisive Strike. When i first found this bug i thought maybe wasn't able to q nexus, but was proven wrong in another game when i did it and realized it was a bug, i didn't think much of it as it didn't happen much afterwards, until today when it cost me a game. I was trying to backdoor, the nexus was basically dead, 2 Q's and a couple of auto attacks and it would've been game, but as soon as i hit my Q, started his Q animation ran at the nexus and just stood there like before, staring at the nexus, didn't do damage to the nexus at all. once cool-down was over i tried it once more, again the bug trolled me, the enemy team was coming at me and they got me, after that they killed my teammates quickly and then they won the game immediately after. I wanted to know if anyone else has experienced this bug. and i hope riot finds a fix to this problem.