Like for example, if i would run behind a running mob i don't hit it but would still get global cooldown and the animation. Or the known "bug" or "lag" as some may call it when there is a aoe circle for example, you get out like 0.5 second or 1 seconds before it ended, you still receive damage.
Both of these bugs are extremly devastating for melees. Especially the first one as you cannot dps while running unless you're literally inside the mobs model.

Other than that. There is a bug where i, as a MNK do for example a Bootshine to switch into the Raptor form. I know for 100% i hit it. But sometimes it takes 3-4 seconds for me to be able to do a Twin Snake or True Strike cause it's still greyed out.

PS: If some do not believe me it's that brutal. I thought so too until i did 3-4 times Stone Vigil. The endboss has alot of AOE. You will notice that he will smack you even though you're out. Which is as you can imagine kinda anoying.