see: https://github.com/neoforged/NeoForge/issues/443#issuecomment-1872934417

Both effects have the same color (16262179, or #F82423), so therefore both effect's chains are the same! Thus, both effects are considered to be equal to each other (by the comparison code). So any change in ordering must happen before the sorting, as the sorting done by Minecraft has no effect to these two effects.

Living entity effects are stored in a map; specifically, a hash map (HashMap). The order of entries of the map isn't guaranteed, therefore the order of entries within the map can change from each run of the JVM. This explains why the two effects (saturaion and instant health) seem to differ in their positions; which one goes first entirely depends on their ordering within the original map.