yes there is 2-3 sec delay while moving.Not being able to hit is when you get "land obstacle" or "insufficient range" . Which means that the target you hit is out of your attack range, or there is something between you and your targer. Usually there is nothing but it still says "Land obstacle". I am not very well with the map coordinate system, but i think that these issues has to do with the 2-3 sec delay. About getting hit from some1 you cant see, there are 2 posibilities.
1) if you are fighting a mob it gets bugged sometimes and you cant see it.( fixes after relog)
2) getting hits in pvp from invisible person. Usually the person hitting you is at your back. And even the map doesn't flash cuz it works only by sight. I mean your screen needs to point the way of the hitter , you wont be seing it otherway.\
Hope that helps