Heimer's rockets not working

I have had a problem in at least 2 games for sure were Heimer's rockets just go through and enemy champion and do no damage. The first time I noticed it, I wasn't sure if I was missing because I was laning against Fizz and I dismissed it as him evading the rockets but I was fairly sure they should have hit. The second and third games I noticed it was against Teemo and Braum. None of them had any items that would have allowed for zero damage. Braum's sheild didn't go up and Teemo has not natural abilities that would stop an ability attack. The rockets seem to be failing to do damage if the enemy champion is in close range. I use Heimerdinger about 90% of the time that I play.