[GAMEPLAY] Skarner E then immediate AA does not stun

I am a Skarner OTP in solo queue. I'm not a highly skilled, high mechanics player, so I don't often notice bugs, or if I do see something buggy I usually assume that it is happening because of some complicated interaction that I don't understand, or that I just didn't see what happened correctly.

However, this Skarner bug, because I play him so much, has become a consistent problem for me. When Skarner uses E on a target in melee range, then immediately follows with an AA, the target does not get stunned as it is supposed to about 25% of the time. I'm only guessing at the percent consistency of this bug based on my personal in game experience, not actual testing in the practice tool.

I heard that Skarner was picked in a pro game today so I immediately went to watch the vod and low and behold, at the 19:50 mark exactly, Skarner E's the gromp and follows with an AA, but the gromp does not get stunned. I slowed the video down to one quarter speed to see if maybe the AA lands before the slow takes effect on the gromp, but I can clearly see the little blue circle around the gromp indicated it is struck by the E and slowed, meaning the next AA from Skarner should stun. But it does not stun.

I've linked the youtube vod and it should jump straight to 19:48 for you to watch.

I started noticing this bug a long, long time ago (maybe more than a year ago) but it was only the past past few months that I realized it was a consistent bug and not something I was doing wrong or seeing incorrectly. Now that I watched it happen in a pro game, I hope this bug can be addressed and fixed.

Thanks! :)