Life leech

I am not sure if this is a bug or not,
however as I was playing my life leach II on Shred was pretty much carrying my life pool up to T12.

Then i changed some gear and some points on the tree and the leach went from carry to beardly noticeable.

If anything I added more physical dmg on the tree.

I went back to T6 just to make sure that i wasn't facing some hidden mechanic but it was not the case.

The gem "works" however the amount leached is in the tens (20-30) while POB says it should be in the hundreds (400).

I also noticed that other people have reported this. Not sure what to do.