Replacing use Ecto.Repo with use Appsignal.Ecto.Repo allows the Ecto instrumentation to keep context across the Elixir processes spawned by Ecto preload queries, ensuring that these queries are correctly instrumented:

defmodule MyApp.Repo do
  # replace `use Ecto.Repo` with `use Appsignal.Ecto.Repo`
  use Appsignal.Ecto.Repo,
    otp_app: :my_app,
    adapter: Ecto.Adapters.Postgres
end

See the changelog for AppSignal for Elixir package 2.8.2 for more information.