Logs full with (ArgumentError) unknown registry: RumblWeb.PubSub

Hi,

after updating to Phoenix 1.5 and follwing the upgrade plan, my logs are full with:

[error] an exception was raised:
    ** (ArgumentError) unknown registry: RumblWeb.PubSub
        (elixir 1.12.0) lib/registry.ex:1332: Registry.info!/1
        (elixir 1.12.0) lib/registry.ex:985: Registry.register/3
        (phoenix_pubsub 2.0.0) lib/phoenix/pubsub.ex:117: Phoenix.PubSub.subscribe/3
        (phoenix 1.5.9) lib/phoenix/channel/server.ex:420: Phoenix.Channel.Server.init_join/3
        (phoenix 1.5.9) lib/phoenix/channel/server.ex:378: Phoenix.Channel.Server.channel_join/4
        (phoenix 1.5.9) lib/phoenix/channel/server.ex:298: Phoenix.Channel.Server.handle_info/2
        (stdlib 3.15) gen_server.erl:695: :gen_server.try_dispatch/4
        (stdlib 3.15) gen_server.erl:771: :gen_server.handle_msg/6

application.ex

defmodule Rumbl.Application do
  use Application

  # See https://hexdocs.pm/elixir/Application.html
  # for more information on OTP Applications
  def start(_type, _args) do
    import Supervisor.Spec

    # Define workers and child supervisors to be supervised
    children = [
      {Phoenix.PubSub, name: Rumbl.PubSub},
      # Start the Ecto repository
      supervisor(Rumbl.Repo, []),
      # Start the endpoint when the application starts
      supervisor(RumblWeb.Endpoint, []),
      # Start your own worker by calling: Rumbl.Worker.start_link(arg1, arg2, arg3)
      # worker(Rumbl.Worker, [arg1, arg2, arg3]),
    ]

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

  # Tell Phoenix to update the endpoint configuration
  # whenever the application is updated.
  def config_change(changed, _new, removed) do
    RumblWeb.Endpoint.config_change(changed, removed)
    :ok
  end
end

config.exs (partial)
…

config :rumbl,
  namespace: Rumbl

config :rumbl, ecto_repos: [Rumbl.Repo]

# Configures the endpoint
config :rumbl, RumblWeb.Endpoint,
  url: [host: "//*.mydomain.io"],
  # root: Path.dirname(__DIR__),
  secret_key_base: "123",
  render_errors: [view: RumblWeb.ErrorView, format: "json", accepts: ~w(html json)],
  pubsub_server: RumblWeb.PubSub

# Configures Elixir's Logger
config :logger, :console,
  format: "$time $metadata[$level] $message\n",
  metadata: [:request_id]

config :phoenix, :json_library, Jason

# Configure phoenix generators
config :phoenix, :generators,
  migration: true,
  binary_id: false

What can i do?

thanks