It seems like whenever exiting the world and rejoining the world, when using with First Aid mod it'll always have a missing heart or so.
Can be tested with Spice of Life : Carrot Edition too by eating to increase max health.

Version 1.18.2

https://www.curseforge.com/minecraft/mc-mods/first-aid

Nevermind, it does work, not sure what causes the heart missing at the first place.