Hey Maelstrom :) Could you provide us with a replay from a battle where you had this issue? This would help us reproduce this one easier

Just to jump in here - I'm noticing the same thing. Specific observations:

• Units will drop orders when pursuing a unit that is leaving a fort. This may be just chasing routing units, but when assigning my unit to chase a unit that is about to flee from a fort, the order will be dropped as soon as the enemy unit crosses the fort boundary. I have to give a manual order to move my unit outside the fort before it will effectively chase the routing unit. (This may also be the case with crossing settlement boundaries, but it's not as obvious.)
• Units will sometimes fixate on one random model when chasing a routing unit. For enemy units that are grouped up it isn't much of an issue, but when the enemy unit gets broken up, my units will often pursue just one model - not the standard-bearer, and not even the closest model. The chasing unit will fixate on one random model, run it down, then say "good job boys time to head back to the tavern" and forget the rest of the unit.
• Units behave more or less as expected when they are right on top of an enemy unit. If they're very close to it (but not across a fort boundary), or even literally on top of it, they'll attack it as expected when an attack order is issued. But the longer the pursuit distance, the more of a chance of the attack order getting dropped. And they often won't pursue remaining bits of units after finishing off the parts of the enemy unit that are closest.
• This is not a guard mode issue, since I play with guard mode off in most cases.

For reproducing, this is easiest to see with fort battles against encamped units. Attack the enemy in the fort, and then when they break, issue orders to chase the routing units, and in most cases, friendly units will drop the orders as soon as the enemy units leave the fort. Fort battles also tend to have units get broken up, which is where the issue with pursuing random models in the unit is more visible.

Not the original poster, but here's a replay with units dropping orders while fighting on a fort map. Friendly units pursuing enemy units through the fort drop their orders at about the 2:00 mark.

I'll see if I can get a replay with units chasing individual models rather than the main body of the enemy unit - that one's a bit more difficult to reproduce.

Bug Report 1.replay

Tried to recreate battle again - replay attached. It is a long battle, so I wrote some notes below with approximate time stamps.

21:25    General (+ another unit) is fighting spearmen. Enemy breaks, new attack order is issued to chase fleeing unit, but order is dropped immediately.

18:05    Swordsmen charge unit trying to flee out gate (near my archers). Drops target almost immediately.

17:42    Same Swordsmen charge another fleeing unit (near my archers). Drops order after throwing javelins and running out of ammo.

11:25    Swordsmen charge fleeing unit (at NW gate). Drops target just before gate.

09:45    Chariot charges fleeing unit, catches it, then drops target.

09:36    Swordsmen next to chariot - same issue.

09:20    Issue new attack orders to both chariot and swordsmen. Both drop orders within seconds.

08:35    Chariot pursues fleeing unit. Drops order as enemy moves out the gate.

07:30    General at SE gate is chasing fleeing unit. Drops order as enemy moves out the gate. Issues multiple attack orders against fleeing unit, but they don't register at all (general is inside the walls, target is outside).

05:40    Chariot charges fleeing spearmen (both inside the walls). Drops target almost immediately. Reissue attack order and chariot successfully reaches target. However, target is then dropped again as fleeing unit reaches some trees (around 5:10).

05:20    General moves outside walls and is later able to target and give chase the rest of the battle with no issue.

Bug_report_Siege.replay

Hey :) Thanks for the detailed information and the provided replays. We reproduced this one and sent it to the team 

I have experienced the same issue in a minor settlement battle. Enemy was in the streets, when I ordered the attack my units (nearby) would make their attack sound and start moving, then stop after a few seconds. I verified that guard mode was NOT active. 

Yes. Same issue here. Minor settlements and forts. In order to chase the enemy outside the fort or settlement I have to issue move orders until the units are clear of the fort or settlement zone, then my units will chase with an attack command. This also happens when trying to issue attack commands within the settlement.