Mods used:

firstaid-1.6.10.jar
TheBetweenlands-3.5.1-universal.jar

Forge version used:

14.23.5.2847

The Problem:

In The Betweenlands, there exists a block named Poison Ivy. Whenever you touch it, it runs a chance to "proc" the poison potion effect. This effect, when procced, affects all player bodyparts at once, causing unintended health loss (usually to half a heart on all body parts). The poison damage is not alternating between body parts, for some strange reason.

This issue was posted to The Betweenlands' before being closed. I have been recommended to post a link to the issue here by one of the developers.
https://github.com/Angry-Pixel/The-Betweenlands/issues/918#issue-520652361