The bug

When you lose the health boost effect, your health replenishes to 20 health points.

How to reproduce

1. Get the health boost effect (/effect @s health_boost 60 3)
2. Take damage until you have less than 20 HP
3. Drink milk or wait until the health boost effect runs out

Observed Result: When you have less than 20 HP and then you lose the health boost effect you are fully healed to 20 HP.

Expected Result: Your health should remain the same after the effect is lost.