TW: Rome 2 (I mistakenly posted it here - can someone please move this post?)
This has been an issue I've seen for years, and I wonder if it is a known ignored issue, or just an unknown one - I would have expected it to be fixed by now.
The Tingis settlement's garrison does not function properly. When you initiate an attack on an enemy where the garrison could reinforce, the garrison or garrisoned army refuses to join the battle.
This also happens if you move an army into Tings, then use another army to attack a nearby enemy. The army in Tingis never joins the battle. You must move the army slightly outside the city to force it to join.
If you have an army inside the city and you are besieged, when you try to attack the besieging army, only the army participates, the besieged garrison never joins the fight against the besieger.
This is so weird!