How to Fix Glow after Update?

The problem about this is that the game has to update the glow status of that entity in order to remove the glow effect.
This doesn't happen very fast for players, so you can still see a laying down entity. That's why you want to write to alpha in order to hide that entity.
You could then check if alpha is 0 and don't write anymore until you reset it again.

The glow status of weapons for example doesn't update at all until you pick the weapon up and throw it back on the ground again.