Colosseum Issue

Hey! I’ve been having an issue on these past two colosseums where I cannot get past the final boss on the first stage in Easy mode. My heroes are definitely strong enough, and I have beaten it in the past. However, the enemies will just get down to the red zone on heath and then stay there. I end up losing the battle because time runs out. This is happening over and over. I have reported this issue, but has anyone else had this problem?