Not op, I think what he means is the session, even when already failed once, can still be used (without error) in the next operation without being invalidated.

Without promise.all, I think it can be replicated like this:

    try{
      await someOp(session);
    catch { }
    await someOtherOp(session);

He expected what the session to be invalidated during someOtherOp.