Leech only applying when monster die?

Ok, I might be crazy and things happen too fast. I will try to capture this clearly in a video. But it is looking to me like sometimes my mana and/or my life leeches are not doing anything or are leeching waaaaay too little. Until a monster dies then my leech comes in regenerating the resource super fast all at once.

leech or %mana/life on kill?

I have 0 life/mana on kill. And the recovery is not instant...

Might be related to my setup. Soul tether with chaos leech from chayula. I also have berserk and life on remnant pickup so my life is constantly fluctuating close to max so that leech can kick in. Same thing also happens when using life leech III instead of berserk.