Can't complete Einar quest (Ruthless Sanctum)

This is not a bug. In Ruthless Leagues, masters such as Einhar do not have guaranteed quest spawns like they do in the base game. This is why the quest log is different in Ruthless, and does not direct you to a specific area.

You can still find them randomly, albeit rarely, or wait until endgame Maps where you can use scarabs or Atlas Missions.