Es+ ghost reaver life leech

I have an issue with my build (poet's pen vd+unearth), have a elder ring with curse poeacher's on hit but seems like ES have a cooldown or something becouse not start to leech instatnly, ES stuck for a few seconds before start leeching.
Why this happend?

First: Poacher's Mark does not grant Leech. It grants Life on Hit, which is something different and is not affected by Ghost Reaver.

Second, the way current Leech is coded in the game is very much a ramp-up mechanic. Each Hit grants a timed Leech Effect, and each Leech Effect can stack, up to a limit of whatever gets you to your maximum Leech Rate (usually 10 with no Leech Passives or item modifiers). This means that strong, slow hits will leech slowly at first, but leech faster after you have landed several hits on the enemy. Fast, smaller hits let you leech faster earlier. If your hits are too weak, you won't see any noticeable leech.

Third: you may be experiencing ES recharge, not leech. ES recharge starts after you have not taken damage* for a few seconds, and is slower with Ghost Reaver than without Ghost Reaver. It stops when you take damage.*

Fourth: Poacher's Mark only grants Life and mana on hits with Attacks, and in this game Spells are not Attacks, so you should not expect your Volatile Dead balls nor Unearth projectiles to benefit from its Life on Hit modifiers.

*technically for the purposes of ES recharge it is take damage or remove ES as there are some things that remove ES but are not damage.

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If you want noticeable Leech from VD, then you may consider using Warlord's Mark curse. A source of fire damage leech may help as well, such as from a Doryani's Invitation, fire flavour. If you wanted to rely on Poacher's Mark for healing you would have to give up on Energy Shield and scale only Life, then scale up your Attack Speed or use an Attack that grants higher hits per second.