Unsure if this was an intented change, so I'm reporting just in case.

Blast protection special attribute generic.explosion_knockback_resistance can now stack for every piece of armor, instead of only applying it for the armor piece with the highest value (highest level enchantment).

This might be expected as per the fix for MC-271573, however there's the side effect of explosions dealing 0 knockback to the player wearing gear with a total of 7 blast protection levels.

How to reproduce

1. Enchant a helmet and a chestplate with blast protection IV.
2. Equip both pieces of armor.
3. Apply yourself a high level of resistance.
4. Place an end crystal in front of you.
5. Hit the end crystal, notice how the explosion doesn't push the player.