Life Flasks occasionally not recovering life- Eternal Youth +Infernalist

I have an issue where occasionally a life flask will be used, but cease restoration as if life is full. This is with Eternal Youth (life flasks restore energy shield instead of life).

I have this happen specifically with Infernalist using Pyromantic Pact (replace Mana with Eternal flame) and Demonic Possession. The flask I am using is 80% MORE life restored when on low life, and .25 charges gained per second. I am also using Coward's Legacy to always be on low life.

I have this issue straight into a new map most often. I will begin casting (and taking damage from max Infernal Flame) and when I hit the life flask, it doesn't apply Energy Shield and I will die to mob damage and Infernal Flame hits. Before I resurrect back in the hideout, I can check the life flask charges and see 67 charges, so it was triggered, but it did not restore anything. I also have caught it in its tracks and checked life flask charges, and seen that charges were used, but not effect applied.

I have no idea what is causing this bug. I can only speculate that the flask effect is marked as completed as if life is fully restored. Perhaps the degeneration effect from Demon Form, combined with life regen causes the flask effect to be sometimes marked as complete?

It also isn't a map modifier such as 60% reduced recovery of life or ES.