Chaos trial unclearable

Having trouble completing even the first round of the trial, where I am tasked with defeating all monsters. An enemy or two will spawn outside of the arena, causing the trial to be uncompleatable. The enemy neither agros nor attempts to move from the top platform. Range abilities will not target the enemy up there on the platform, either. Granted, a warrior doesn't really have the range to do so in the first place. I would love to attach a screenshot to this, but I do not see an option to do so.