Trouble with assassin perma-stealth

[Myboot]

Alright so I'm a little trouble with perma-stealthing as assassin. Basically the enemy notices me too quick when I try to hook kick or shadow dash to them. Sometime they take about a second or two to notice me but other times the enemy notices me instantly which is really frustrating when fighting against a boss. BTW my ping is around 200-250ish so that might affect it a bit. I just wanted some feedback on if other people have this problem or not.