Mobs no longer get repelled by shields

The bug

Ever since the beginning of 1.14 snapshots, mobs wouldn't get knocked back when a player is blocking with a shield.
Here are some screenshots from the current version (1.13.2) and current snapshot (19w14b)

1.13.2:

• Vindicators
• Piglin (New Mob in 1.16.x)
• Zombie Pigman/Zombified Piglin (renamed in 1.16.x)
• Zombie Villager
• Zombie
• Husk
• Drowned
• Wolf
• Wither Skeleton
• Enderman
• Spider & Cave Spider
• Silverfish
• Slime and Magma Cube

These mobs do knockback when you're blocking.

19w14a & b and beyond of 1.14 - 1.16:
The mobs I said above don't do knockback in the current version(s).
However, this doesn't affect to Creeper/TNT explosions, as you still do knockback from it. And arrows from Skeletons/Strays will still bounce of the shield.

Code analysis

Code analysis by Maity & Fuzs can be found in this comment and this comment.