If a players max health is above 20 and they die, when they respawn, they have 20 health instead of their max health.

steps to reproduce: 

1. change max health with /attribute @s generic.max_health base set 40
2. die using any means necessary (/kill if you want)
3. respawn, and see that your current health is 20 instead of 40, and you need to regenerate the rest