I've been informed that when the player is the third party on the quest Caravan Ambush or when the player is not the faction leader on siege defences or the player is not the owner of the sieged settlement on defence the order of battle is disabled. It is intended, not a bug. Thank you for reporting.
The worst part of this "Excuse" is that you can still tell your troops where to go after the battle starts. You just don't have the ability to make deployment choices before the battle starts. This is just nonsensical. You are telling me that I can't pre-deploy because I don't own the town or I didn't start the battle, but then I can suddenly retain command of my troops during the battle. It is literally just an unnecessary removal of a feature.
I understand not being able to redeploy local militias and garrisons and siege engines if I don't own the settlement or I wasn't the one who started the siege, but what about my troops? What about just my character? Am I not free to put myself where I want? Am I not a mercenary ranked above the common soldier and paid by the faction leader? And what about instances where I come to the aid of allied parties? Why do I lose the ability to redeploy? How can the lords engaged in battle know that I was coming and then proceeded to deploy my troops for me? Furthermore, the army system exists and works fine for confined deployment. What was the point of all this?
The same applies for the removal of music in hideouts. I remember the nonsensical reason from another dev response was "its a stealth mission. so music was removed," but I apparently my character yelling "TROOPS" at the top of their lungs was not loud enough to alert the bandits.