So on the overworld map I can get deadlands assassin to proc absolutely reliably. I can run up to something, heavy attack it, whoosh there's a fan of knives and it shows up in my combat logs.

Against a trial dummy in a player home, or against any enemy in a dungeon (for example zenithar's abbey) I cannot get it to proc under any circumstances. Unsure if it's related to the monsters themselves, the map, or has something to do with zoning. No visuals and no appearance in the combat log.