As of 4/19/24, it seems that the Ghoul Rictus enemy (not the alpha, where drops seemed to be working properly as of the latest ghoul purge), is not dropping mods and shows no mods as drops in its codex entry or online drop tables. Since (in my understanding) this enemy is meant to be the only current source of the Butcher's Revelry stance, this is likely an impactful error if it is indeed impacting more than just the listing but also the actual possibility for the mod to drop in game.