Scold's Bridle + Bladefall of Trarthus with flask life leech effect

https://youtu.be/gL1leg0OHJM

By pairing it with Scold's Bridle helmet, the self-damage from the mana drain can reach a threshold that triggers a flask enchant "15% of Damage Taken from Hits is Leeched as Life during Effect".

However, during testing I ran into a strange issue. In the video, you can see that my build works:
Using Divine Flesh, I convert half of RF’s damage to chaos, balancing out the sustain.
If RF can be sustained, it means life leech from the flask enchant is working.

But when I cast other skills, my life suddenly drops quickly.
I suspect that either the life leech or Tainted Pact’s effect is gone.
My guess is that the Scold's Bridle's self-damage from that skill cast is one of the reasons.

(Afterward, I tested by linking Life Tap and the issue didn’t occur, confirming this was the cause.)

The confusing part is: why would the life leech stop?
In the video, I tested with Petrified Blood, so it’s not caused by hitting full life.