Server Version: PAPER 1.16.5
OldCombatMechanics version: 1.11.0
Server Log File: ---
OldCombatMechanics config file: https://pastebin.com/JEV4imS5

Steps to reproduce the behavior:

1 versus 1 with a player with full diamond armour with protection 4 and unb 3 (or netherite armour with the same enchantments)
hit on the player and causes 0 health points
just causes lost health points when you take off a piece of the armour
we used sharpness 5 on the swords (diamond and netherite)

Please try this with the latest test version, many changes have been made since 1.11 to address the damage calculations.