Spoils of War Passive with Kalista Soul-Marked Bug

I was playing Maokai support with Kalista, and suddenly in the middle of the game the Spoils of War passive stopped working. I have a feeling that it is a conflict between Kalista's Soul-Marked ability, but I am not sure.

I also noticed when I was near Kalista every once and a while my graphics would become very slow. I didn't check my FPS, but it definitely did not look like a network lag issue. Next time I play with Kalista I will try to reproduce and update here.