The issue here is I'm playing in a modpack with First Aid, Apotheosis, Corail Tombstone, Werewolves and Vampirism and a bunch of other mods. Whenever you get anything that modifies your hp, the first aid mod scales the hp to make it so you take damage, etc. adding armor that boosts your HP, or changing into a werewolf that increases your maximum hp. Whenever hp is removed, taking off the armor, changing back into human form, health boost effect runs out, etc. the player isn't reset to max hp of your normal hp, the hp they lose counts as damage and sometimes flat out kills the player resulting is a pseudo death where the player dies, no death message is displayed in chat, and a gravestone does not generate for that player.

I'm playing with 1.18.2 Minecraft on firstaid-1.11.1.