Essence Rush gives no leech

I think I am going mad, but it seems like I am not able to leech at all with my character.

I have Essence Rush allocated. POB says that time to reach cap of 2,237 ES is 0.8 seconds. Which tells me that in less a second i should be full ES (I have 2,736 ES), but what happens instead, monsters hit me takes my life to half and I don't recharge for a few seconds and start recharging from the normal ES recharge.

Maps tested do not have "can't leech" mode. Is it something in my build blocking the leech?

#3,725,137,686

Edit: Also using Ehereal Knives which is a spell, leech is not mentioned anyware in tooltip or in the caracter stasts for EK.