These unnerving daemons represent death by direct assault against a soul or life-force. Rarely seen in the mortal Universe, astradaemons spend most of their time hunting the pathways between the living world and the afterlife. There, they capture migrating souls, snatching them from their rightful rewards or punishments and dragging them to Abaddon as tribute to their undying masters. These horrifying predators of the dead can also be found stalking the banks of the River of Souls in the Astral Plane, where they constantly hunt for new victims.
Devour Soul [one-action] (divine, incapacitation) Requirements The astradaemon hasn't used an action with the attack trait yet this turn; Effect The astradaemon draws out and consumes the soul of a living creature they have grabbed. The creature must succeed at a DC 35 Fortitude save or instantly die. If it dies, the astradaemon gains 10 temporary Hit Points and a +2 status bonus to attack and damage rolls for 1 minute, or for 1 day if the victim was 15th level or higher. A creature that survives is temporarily immune for 1 minute.
It's bizarre, but the 1e stat block seems to imply it's intentional. That older stat block does a much better job explaining why the consumed soul could be brought back.
Devour Soul (Su) As a standard action, an astradaemon that begins its turn with a grappled opponent can attempt to draw out and consume the soul of its victim, killing it instantly. This ability only works on living creatures, which may resist with a DC 25 Fortitude saving throw. The save is Constitution-based. For every 5 HD of the slain creature, the daemon gains a +1 profane bonus on attacks, saving throws, and checks for 24 hours. This ability does not consume all of the soul, and pieces of it still exist after the daemon completes its feast (enough to be able to resurrect the slain victim normally).
One of these things is talking about souls on their way to judgment, the other is rules for eating souls of living PCs - whose souls survive the process to join the river of souls, where they can qualify for a more permanent digestion.
I agree it's not really given enough explanation, but agree with Xenocrat. The first is talking about hunting loose souls on the river to judgement. The second is consuming part of the soul of a living creature.
It's less a "devour of a soul" and more "steal soul essence from living creature that also kills the creature".
