Steps to reproduce the issue

When attempting to heal players via:

/effect give @a minecraft:instant_health 1 32

The effect is as strong as:

/effect give @a minecraft:instant_health 1 0

This gets even weirder where amplifiers 29-31 produce no health healed. Then amplifier 32 heals as if it were amplifier 0.
This is true of all modifier values where:

modifier = modifier % 32 + 1
if (modifier > 28) {
  modifier = 0
}

so 29-31, 61-63, 93-95, etc. → heal 0 hearts.

Expected result

The player should be healed by the direct modifier value

Actual result

The player is not healed, given the condition specified above.