Kayle's E (Righteous Fury) bug with towers

So today I played a feature game, Legend of the Poro King, as a Kayle, and I noticed when I activated my E, I almost didn't deal any damage to the tower.

I think the damage that I dealt was only the bonus damage which I got from E, and my base attack damage just didn't apply.

I'm playing on EUNE, and I "recorded" the game with op.gg, so if you want to check the circumstances you can download the bat file. This incident happend around 15:20, during the siege of the 2nd tower.

(Maybe later I will upload a vid about it, but don't count on it.)

I hope somebody can either explain what happened, or fix this. Thanks for your time.