I found a bug

I built a huge African savannah habitat (over 2000m2). The habitat contains zebras, springboks and all of the compatible animal species. It has wooden non-custom borders with windows. But when I put the animals in they escaped immediately. The black wildebeest just ran straight through the border. Not breaking it, like it doesn't exist. I have paused and unpaused an reset the game and it still happens. How do I fix this?