Bludgeon....

It is hard to deliver a death blow with a bludgeon. One has to use auto-attack for this or use something else. One can only kill something with a bludgeon glyph when this blow does not also add a stun effect to the opponent. Other glyphs/spells/effects will do 0 damage when the opponent is stunned and the blow has done more damage as the opponent has hit points left for a short time. For animals it seems one has to wait until the stun effect is gone before a killing blow can be applied.

On Knock-back many mobs are taken out of combat, especially seen with animals. This activate their speeded self heal capabilities. The are also not targeted any more this prevent auto-attack from working. If they are at low hit points you can not kill them with a bludgeon glyph as long a stun affect is also applied, usually you wait for the auto attack to do the job, but...
This also happens sometimes with other bludgeon glyphs that have a chance to stun the opponent.

If there are problems with the host of the instance knock-down does not work. You can see the "knock down effect" on the opponents bar, but they are not knocked down.