Stop-gap sheild bugged?

Doing deathless relic stopgap build on Moe’s stop Gap never gives the damage immunity it says on it

It triggers at 50% HP, you have to full heal before each trigger. Stop-Gap makes that impossible

Stop Gap shield has nothing to do with health it’s when Sheild breaks become immune to damage for 5 seconds

Sorry I was thinking of the imunity relic for some reason