Shyv Q making autoattacks disappear?

I was playing a ranked game earlier, and sometimes I noticed that my q didn't deal damage. Seemed weird, but I ignored it at first. Then it just kept happening. Happened at least 10 times that match, even when fighting champions. There were a few kills I didn't get because of it. I have no idea what causes it, but sometimes when you q the damage just disappears.

I've no idea what causes it, if it's a sated bug, or whatever. Hopefully someone can find out. This is really sad because I main Shyvana.. :(