Gameplay Bug: interaction between Rakan and Kalista's W passive

I don't currently have a screen shot and I am not sure what triggers it. During multiple games where I was Rakan and my ADC was Kalista, I would auto-attack a minion that she put her passive on and the passive did not proc. Later in the same game however, it would start working properly again. This would happen on and off through the game where sometimes Kalista's w procs and sometimes it doesn't. I tried melee range and max range and neither made a difference in this event. I also did not notice the bug happening on champions.