Knockback enchantment has no effect on players

Steps to reproduce:
1. Acquire a sword with the knockback I enchantment and a sword with the knockback II enchantment.
2. Switch all players to survival mode.
3. Hit another player with each knockback sword, and then punch it.

Expected results:
The other player gets knocked back farther when hit with a knockback I sword than with a punch, and farther with a knockback II sword than with a punch.

Observed results:
The other player gets knocked back the same distance (~3 blocks) by a punch and by knockback I and knockback II swords.

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Original title and description
Frost walker and knockback enchantments

Both enchantments are not working