It happened in my game too, 350 turns in, having a really enjoyable game up to that point, did spot some bugs but nothing game-breaking until this one. Magnar was getting a little big for his breeches, he built all 3 towers and was now building the Overlord Forge so I had to rush my army to take out his capital, where the towers were and sure enough I ran into defender spawn spam. This is a ridiculous bug, I don't understand the cause of it. They have a grand total of about 60 units inside the battle, I can't even attempt to fight the battle normally because it just hangs forever on the enemy because I'm assuming they can't move due to most of them spawning off grid, and I can't auto-resolve it either because my best army gets crushed. The precise breakdown of Enemy Units is as follows: 2 Guardian Statues, 19 Guardian Idols, 27 Assassin Demons, 3 City Milita, 2 City Archers, 2 Thrall Archers, 2 Slave Cavalry, Nochd Nightbringer, Rostyra, and Shimsher. I will happily provide screenshots and a save game upon request.