I wrote this for “pub-sub” testbeds.

  def handle_info({TestBeds, [:testbed | _], _}, socket) do
    {:noreply, assign(socket, testbeds: TestBeds.list_testbeds())}
  end

I replicated it for alerts:

  def handle_info({Alerts, [:alert | _], _}, socket) do
    {:noreply, assign(socket, alerts: Alerts.list_alerts())}
  end

Nope!
I accidentally set the code like this:

  def handle_info({Alerts, [:alert | _], _}, socket) do
    {:noreply, assign(socket, alerts: Alerts.list_testbeds())}    # error should be Alert.list_alerts
  end

In the post above I wrote that the code is identical between the testbed and alerts. It forced me to fine-tooth that statement. They weren’t identical. The console had a non-red highlighted error but it was tangled in the rest of the output and I missed it.