Holy Flame and Sakura passive don't stack

Nidhugg

If Sakura (SR healer/support) wears the 4pc Holy Flame her passive heal seems to prevent the trigger of Holy Flame when she is under 30% hp. I have reproduced this many times, as she is usually my last support alive for difficult encounters. One such encounter the enemy would deal 500ish damage per attack, which was slightly more than my passive healing of 15% hp while under 30% hp. I noticed however that she would sometimes not regain her health back at all, after multiple turns, eventually dying.