Lux won't auto attack bug

I really don't have much to back up what triggers this, but I'll give as much information as I can. For some reason, very rarely, Lux will refuse to auto attack. This was pre-the latest patch, and it only happened in two games, but it is pretty devastating when it does happen. The first game, if I Qd the enemy fiora and she Wd it, occasionally I wouldn't be able to auto her (i am aware that my auto will do nothing during her cast, but this also extended for about three seconds after the initial cast). This also repeated itself in a recent game against Karthus. It only happened once however, again after a Q. I suspect it may somewhat be linked to slows, as I believe I was slowed by karthus's wall at the time, and may have been slowed by fioras W post cast as well. Wish I could give more information, but thats it so far.

I consider myself a Lux main and also somewhat competent at the game, so while skepticism is welcome or suggests for why it may have been a problem on my end are welcome, I doubt it was a problem on my end as it happened repeatedly in the fiora game. This also only happened when they were sub 30% hp. Not sure if linked.