What is your ping sir?

Thats weird. But something that I know when my nornal attack miss or got delay is due to my character has a low *attack rating. Open your character tab, hover your mouse cursor on attack, it will then show your chance to hit the targeted monster.

About the potions, the effect are normally kick in immediately, but it will replenish over time and not instant (except for full rejuvenation potions). However, if you use a potion and still taking dmg at the same time, the healing progress will be very slow.