We can check how the code was developed by using quote do

quote do
  if Enum.any?(x, & &1 == "A"), do: 3, else: 2
  |> IO.inspect(label: "returning a")
end
|> Macro.to_string()
|> IO.puts()

That results to

if(Enum.any?(x, &(&1 == "A"))) do
  3
else
  2 |> IO.inspect(label: "returning a")
end

Which is always true in this case. So, it won’t enter into else

I’m still seeing the issue with elixir 1.11.2-otp-23 and erlang 23.1.5

Can confirm - Axelson’s example works fine on my machine (OTP23.1 / Elixir 1.11.2) and this one fails.

A colleague tried @LostKobrakai’s example on 22.2.6 / 1.11.1 and it printed 2 three times, as expected…

Poked at it a little more. Strange things are afoot - I get different results depending on what’s on a line that never executes (OTP 23.1 / Elixir 1.11.2):

defmodule Dummy do
  def execute(x) do
    with var_a <- get_a(x),
         var_b <- get_b(x) do
      IO.inspect(var_a, label: "a")
      IO.inspect(var_b, label: "b")
      IO.inspect({var_a, var_b})

      if var_a != var_b do
        IO.inspect(var_a, label: "a")
        IO.inspect(var_b, label: "b")
        IO.inspect({var_a, var_b})
      end
    end
  end
  defp get_a(x) do
    IO.puts("get a")
    if Enum.any?(x, & &1 == "A") do
      3
    else
      2 |> IO.inspect(label: "nope")
    end
  end
  defp get_b(x) do
    IO.puts("get b")
    if Enum.any?(x, & &1 == "B"), do: 2, else: 1
  end
end

Dummy.execute(["A", "B"])
# prints
get a
get b
a: 3
b: 2
{3, 2}
a: 3
b: 2
{3, 2}

But commenting out |> IO.inspect(label: "nope") makes it do the {3,1} thing…

EDIT: bonus fact - the 1 has some kind of additional significance, changing it to anything else makes the bug stop happening on my machine.

I simplified the example to this and can still reproduce the odd print running macOS Catalina 10.15.7 using Elixir 1.11.2 and Erlang 23.1.5.

defmodule Dummy do
  def execute(x) do
    with a <- get_a(x), b <- get_b(x) do
      IO.inspect(b)
      if a != b do
        IO.inspect(b)
      end
    end
  end
  defp get_a(x) do
    if x == "A", do: 3, else: 2
  end
  defp get_b(x) do
    if x == "A", do: 2, else: 1
  end
end
Dummy.execute("A")
# 2
# 1
# 1

Simplifying it one step furter, replacing if x == "A", do: 3, else: 2 (that will always evaluate to true) into if true, do: 3, else: 2 will fix the unexpected output.

defmodule Dummy do
  def execute(x) do
    with a <- get_a(x), b <- get_b(x) do
      IO.inspect(b)
      if a != b do
        IO.inspect(b)
      end
    end
  end
  defp get_a(x) do
    if true, do: 3, else: 2
  end
  defp get_b(x) do
    if x == "A", do: 2, else: 1
  end
end
Dummy.execute("A")
# 2
# 2
# 2