When you take damage from anything, your health will regenerate depending on your food bar level but, you can't regenerate back to 20 (10 hearts) hp. Instead, you will have 19/20 (9.5/10 hearts) health points. The only way to get back to 20 hp (10 hearts) is to use a potion.

Steps to reproduce:

1. Create a world in survival.

2. Take damage from anything.

3. If you lose Food Points from damage, eat anything.

4. Your health points can't go past 19 (9.5 hearts) .

Expected Results:
Your hp would regenerate to the maximum hp level.

Observed Results:
Your hp will regenerate until it reaches 19 (9.5 hearts) .

I've been planning on going to an ocean monument but at 19/20 (9.5/10 hearts) hp, I'm not taking that risk.