Garen's abilities dont trigger

when i was playing Garen for the past 2 days, i realized at times his abilities dont trigger. for an example, i was fighting jayce top lane and me and my mid laner (Diana) dived for the kill. i flashed and ulted and you can see the animation but no damage was done. another time i was chasing an illaio and as i Q her no damage was dealt, i had to follow up with few auto attacks to finish her. At first i thought i missed something but after it kept recurring 3-4 times per game. Would like to know if anyone else is have this problem or if its just me.