I think it's all pathfinding issues, I've seen all of those and on Vladian castles specially when your soldiers set up the tower they start to run towards the wall and get stuck under the tower instead of climbing.
''This is kind of a bug, but I think the siege battles need its own commands such as, 'Break the gates' or climb the ladders.'' Click F1 and point towards the gate or the ladders,the icon will change and they'll ''try'' to do it,sometimes they do sometimes they don't.