Akali's destination is computed on Shadow Dance activation. Thus, she dashes towards the target's saved location which in most cases will deviate from the actual position the target holds when she arrives.
Prior to patch V5.9, Akali was placed directly on top of the saved location. Thus, any deviation affected Akali equally in all directions. Whether the target moved towards Akali or away, did not matter. Only the actual distance traveled by the target decided whether the AA would land or not. In almost all cases, Akali would be able to perform the basic attack.
Hence, Akali's threat range was a circle of 125 units around the target's saved location.
Now Akali strikes through the target and dashes 150 - 250 further, placing her on the far side of the target. Thus, her destination has shifted by the same amount. A smart enemy can use this to their advantage. By moving towards Akali when you expect her to Shadow Dance, you can effectively prevent her from detonating Mark of the Assassin. This strategy works by making use of the uneven distribution of her threat circle around the target location.
Most of Akali's threat is now centered behind the target. If an enemy tries to move away from Akali, Akali will have a significantly easier time to detonate Mark of the Assassin since the enemy has to cover a significantly greater distance (~ twice her AA range + Akali's diameter) to escape her threat zone. Meanwhile, if the enemy moves towards Akali he only has to cover approximately 100 - 25 units (AA range - distance placed away from target).
I suggest rectifying the situation by increasing Shadow Dance's missile speed so that the target's position at Shadow Dance activation more closely matches the target's actual position when Akali arrives.