It is all specs. For Legion they changed when attack information was locked in. Until now the instant you used an ability the damage was locked in no matter how long it took that ability to hit the target. Now it isn't calculated until it actually hits the target. It is a rather large change because it alters how people potion or time use items like rings, necklaces and trinkets. Even if you have insane lag or other issues it doesn't change how the system works just how it appears on your end do to lag disguising the chain of events.