Black corners or a smudge may be due to various reasons and can be resolved by trying out different steps.
If your video feed has a smudge. Check first if there's still a plastic protector covering the camera lens, you may then remove this.
Or if your dog has licked the lens, just try to wipe it out.
But if you are seeing a black corner as shown in the photo:
Please try to adjust the outer camera lens to make sure that it's in place.
If this doesn't resolve the issue, please take a picture or video sample and contact Customer Support.