channel.ex

def join("room:" <> room_id, _params, socket) do
    #this prints
    IO.inspect(room_id)

    case RoomCtx.find(room_id) do
      nil ->
        #does not print
        IO.inspect("not found")
        Logger.debug("[channel:room] attempted to join nonexistent room #{room_id}")
        {:error, :not_found}

      room ->
        #does not print
        IO.inspect("found room")
        room = Repo.preload(room, :subscriptions)
        do_join(socket, room, is_subscribed?(room, socket))
    end
    |> post_join()
  end

ctx.ex

def find(id) when is_binary(id) do
    #this prints just fine
    IO.inspect("Getting id #{id}")
    Repo.get(Room, id)
  end