This maybe happens because for some players who always run to escape your hit like boba fett with his jetpacks and for the well-known coward , Grievous.
By your description it seems to me your experiencing a LAG issue. And before anyone assumes they know everything about LAG, LAG may take many forms. One of them is caused by ping disparities.
Each action on your client must be sent to the server, and then resent to the other client. The same for your foe's actions. This means that many times, if your ping is high enough, either your enemy appears to be in a place that he already left, or you believe to be somewhere, just to be brought back to a prievous place through a mysterious warp.
As the server is the one who dictates the rules, if your client happens to be showing things that are either a past situation, or a situation not yet processed by the server, it'll correct those based on other situations happening for it.
This explains slashing an enemy and not hitting him, and this also explains leaving an enemy just to be hit through an unbelievable distance (or even be brought back to a prievous place to take the hit).
However, and here comes the best part, I already experienced Palpatine and Luke doing incredibly far hits, that have nothing to do with LAG. Enemy players across the map taking hits from these 2 characters as if they were in close quarters. As I have no idea how to reproduce this yet, and it occurs very rarely, I didn't report it yet.
