So the Blood Pact node makes Drain Life cost no mana, instead you lose 10% of current health per second. Soul Stability meanwhile puts a -100% modifier on all health drain while Death Seal is active. This does stop the health drain from Blood Pact, however if you’re still continuing to channel Drain Life when Death Seal ends, you still maintain that -100% health drain effect from Soul Stability. So you have a free channel until you decide to move. (This is the same regardless if you start channeling Drain Life before you activate Death Seal, or if you start channeling it while Death Seal is up)
Also if you take the Unclosing Wounds passive, the health drain part of it normally stops when you have Soul Stability taken, and Death Seal is up. However, if you’re channeling Drain Life while you have Blood Pact taken, and then go into Death Seal with Soul Stability chosen, the health drain from Unclosing Wounds will still continue while you’re in Death Seal. (This only happens if channeling Drain Life before you go into Death Seal, and stopping the channel of Drain Life does fix it. It doesn’t start the health drain from Unclosing Wounds again, if you do restart channeling Drain Life, until Death Seal Ends(though then you do still have a free Drain Life channel as per the first issue))
I imagine the first part is just an issue with snapshotting, so wasn’t sure whether to post it as what I’ve heard from a dev is that snapshotting isn’t a concern. However the second part is possibly a result of that or something, and a bug (as it makes the skill node not work as intended, and I’d imagine the same effect could be seen by other forms of health drain that Soul Stability is meant to stop)