Path of Exile Dev Tracker

After a lot of testing i concluded that this item must transfer life leech instances from mines to you. Means that if you detonate a mine that hit enemies you only get life leech if you already have UNdetonated mines on the ground at the same time

That is definitely not at all how it works. The only leech instances involved in this mechanic are applied directly to you, not to the mines, and leech instances cannot be moved from one thing to another.

If for example you simple throw a mine and detonate it you ll never get life leech.

This is incorrect. A single mine can and does correctly apply a leech instance to the player for each thing it hits. I have tested this in-game and it is working correctly. The amount of the leech will be low from an individual mine, but it does occur.

There is no distinction at all based on where you get certain bonuses from, nor a sequence which this can interrupt to get a value.

Conversion (gain x as extra y is a special case of conversion) applies all modifiers that would apply to either x or y (in this case life or energy shield). The "increased" and "reduced" modifiers stack additively with each other, because that's how those modifiers work. But increases are not the only kind of modifiers.

CI's "value is exactly 1, no exceptions" is also considered a modifier to life. As such, it also applies to the ES which is being converted from life, and sets the value to 1.

No, because you still take the damage first. If the hit kills you, you'll die before leeching anything.

If you survive taking the damage, you'll regain some life. But you do need to survive the full hit.