Lost a battle because my reinforcements never spawned in!

Was playing wood elves when some "forest invasion" battle-event popped up. Sent my armies over to deal with it. My main army was to reinforce a tiny one. Problem is, despite the pre-battle screen & minimap telling me where the reinforcements were to show up, they never arrived. No way of winning now, so I had to retreat my tiny army. Despite having no units on the field, the battle wasn't ending, so I had to concede the battle to leave. Am I missing something or is this a bug?

Was an unfortunate bug for me since my main army was on forced march, so conceding the battle caused the entire army to die. Guess this could be caused by a bug from another mod or the main game but I've never had this problem before and this is the only major mod I have installed.