Env variable is nil when passed through plug opts on runtime when using release

Hello, so I have few apps under an umbrella, lets say the names are linesdk, hibiki, and hibiki_web. So linesdk have a plug where you pass a secret key as the opts. hibiki_web is the app which runs the cowboy server and routes request to the linesdk plug. The secret key that needs to be passed is inside the :hibiki :channel_secret config. Here are some snippets

defmodule Hibiki.Config do
  def channel_secret, do: Application.fetch_env!(:hibiki, :channel_secret)
end

defmodule HibikiWeb.Router do
...
  post("/hibiki",
    to: LineSdk.Plug,
    init_opts: [
      channel_secret: Hibiki.Config.channel_secret(),
      handler: Hibiki.WebhookHandler
    ]
  )
...
end

defmodule LineSdk.Plug do
  use Plug.Builder
...
  plug(:validate, builder_opts())
...
  def validate(
        %Plug.Conn{
          assigns: %{raw_body: raw_body}
        } = conn,
        opts
      ) do
    with {:ok, signature} <- get_signature(conn),
         {:ok, _} <-
           LineSdk.Auth.validate_message(
             raw_body,
             opts[:channel_secret],
             signature
           ) do
      conn
    else
      {:error, err} ->
        conn
        |> send_resp(400, "#{err}")
        |> halt
    end
  end
...
end

And the plug access the channel_secret using opts[:channel_secret].

Now, these piece of code is running fine in my local development. But when I build the release into a docker image and deploy it, somehow the opts[:channel_secret] became nil while the opts[:handler] is not changing.
The weider thing is when use the release binary remote command and run Hibiki.Config.channel_secret() it does returns the correct value.

This is after I refactor the plug from hibiki_web to linesdk. Before it was fine. But in both cases, it is still the hibiki_web app that calls the Hibiki.Config.channel_secret() but somehow when the released app is running it returns nil. Can anybody help me? Thank you very much!