The chest breaking logic is really simple at the moment. It does a line of sight check as well as a distance check before using the skill. Sometimes, the LoS check fails, causing the bot to go up and break it.
Ideally, we'll have to add custom logic based on the skills being used, since some of them can be cast anywhere on the target, such as Cold Snap or Leap Slam, whereas others need direct line of sight, such as Fireball.
So that is something we are aware of and will be "advancing" in the future, logic wise, but for now, that's why that happens.