I have seen this bug happen countless of times since i started playing X years ago, it usually happens with ranged enemies and when playing a melee class.
You click on a ranged mob to melee-attack, but instead of going towards the monster the player character moves away a few cells and waits 1~2 seconds, then the monster position gets updated, and ater the position update the player character finally runs to the ranged enemy and attacks.
It probably has something to do with too slow monster position updates from the server/the server not sending position updates fast enough.
Edited by Atum, 18 August 2015 - 09:55 PM.