Same, waiting months for a fix on this and the mixed troop types in the same group in sieges. It is a core feature and making it playable should have priority over minor polishes and new features.
I get this problem in every siege for a couple of months now, no steps needed to reproduce it for me, simply starting a siege and the army becomes 2 groups of equal number of mixed units, one "archers" and the other "infantry" but there is a mix of archer,cavalry and infantry in both groups, and...