The bug
Due to the change (fix of MC-44192) in 20w06a, in which knockback resistance in now a scale instead of a probability, ravagers can easily be knocked back with a sword that has the knockback enchantment, which makes them slightly less tougher than before.
Not only this affects ravagers, but other mobs like hoglins and mobs with knockback resistance (via attirbutes and commands).
How to reproduce
Have a sword with the Knockback (II) enchantment
Spawn a ravager and kill it
→ ❌ Observe that the ravager always receive full knockback from the sword with the enchantment, rather than half the knockback.
You could already deal knockback to them with sprint-hits.