I’ve been setting up my first Phoenix deployment on gigalixir. I’m deploying with mix, and I was having some trouble, so I did an iex -S mix to practice at home. That resulted in this:

[info] Application crit exited: Crit.Application.start(:normal, []) returned an error: shutdown: failed to start child: Crit.Setup.InstitutionSupervisor
    ** (EXIT) bad child specification, more than one child specification has the id: "critter4us".

mix phx.server also fails. I now get the same failure for a git revision from a week ago, well before I started to deploy. Moreover:

• I did both a mix clean and removed the _build directory.
• It happens with a new shell (so not an environment issue).
• I hadn’t changed the version of Elixir or Erlang I was running. (Both are up-to-date.)
• ps shows that there are no Erlang processes running.
• Anyway, the app is not distributed. It’s a very basic Phoenix app.

For what it’s worth, the application.ex looks like this:

    # List all child processes to be supervised
    children = [
      # Start the Ecto repository
      Crit.Repo,
      # Start the endpoint when the application starts
      CritWeb.Endpoint,
      # Starts a worker by calling: Crit.Worker.start_link(arg)
      Crit.Audit.ToEcto.Server,
      Crit.Setup.InstitutionSupervisor,
      {ConCache, [name: Crit.Cache,
                  ttl_check_interval: :timer.hours(24),
                  global_ttl: :timer.hours(48)]}
    ]

    # See https://hexdocs.pm/elixir/Supervisor.html
    # for other strategies and supported options
    opts = [strategy: :one_for_one, name: Crit.Supervisor]
    Supervisor.start_link(children, opts)

The problem is definitely around InstitutionSupervisor. If I delete it from application.ex, mix phx.server starts.