The Invulnerable datatag is not working

I attempted summoning an invulnerable slime with the command
/summon Slime ~ ~ ~

It was just a normal Slime, I could then kill it just using a sword, I then tried it with different mobs, and no difference in results. I looked around on the internet to see if I was doing it wrong and everyone had the same command.
/summon WhateverMob ~ ~ ~

But nothing worked

Steps to Reproduce:
1. Attempt to summon any mob that cannot be killed by melee damage (not /kill or tp to void, etc.)
2. /summon Slime ~ ~ ~

3. See if it works or not.