” A real beis din cannot convene a session without both parties present.”
That is indeed the halachah. But in addition to this example, beit dins in Israel have pasuled conversions without the convert being present. This is worse than the stuff the Conservative movement does.
This was charliehall’s comment above. There is a comparison here that is wholly inaccurate. On matters that are of a din Torah between two litigants (??? ??? ??????), there is a distinct obligation of ???? ??? ????? which requires that both litigants be present before any of the dayanim hear any of the complaints. If the matter is an individual psak, such as the validity of the ?????, there is no such requirement. Such a matter does not involve a litigant, but rather a halachic process that is being evaluated as valid or not. Nice try.