In CAS my pets will freeze and glitch

So, my sims 4 was working great, and I downloaded cats and dogs. I was super excited and ready to create. then, as I was working, half the screen would stay blue, and the other half would look like a blank terrain. I thought it was a different background, like in the sims 3 pets. Then, Some parts of the pets became black and the whole screen just froze and the only way I can close it is if I restart my whole computer. Please help.