
Here we have a Commoner and the SOUND of a Soul Reaper there, as well as the Worm Cultist spawning, but the Reaper itself has to be INSIDE the cliff. I ran all around looking for the thing, but, nope, it's in the cliff.
Map location is here:

On that note, I've rarely seen any Soul Reapers spawn outside of Solstice, and even those that do spawn in Solstice are rare (believe me, I've checked). Could you at least increase the spawn rate?