These have been bugs for a very long time.

If you trigger a lumber to attack you while there's a block or wall between you and the Lumber, the Lumber deals no damage, but still deals the massive knock back they do if you are in range of the attack. (Although other enemies that have heavy, high knock back attacks don't cause this to happen - or any other enemy for the matter)

When Greavers attack, they leave a status mist where they attack. This status mist bypasses solid walls or blocks. Is it not possible to have the mist require Line of Sight like every other bomb?

Gremlin Bombers are able to throw/shed bombs through solid walls or blocks, there's not much more to it, it's just how the game places their bombs.

These bugs make normal content very irritating to play, and even more so during the Winterfest's Grinchlin Assault mission where there is an abundance of all three of these enemy types.