When building this app "AR Drawing" we had to use ARKit and SceneKit, there can be several challenges that we faced, some of those were:

1. Device compatibility: ARKit requires a device with an A9 or later processor. Therefore, we had to make sure we tested this app on latest iPhone 13 Pro which has LiDar sensor for better mapping.
2. Performance optimization: This AR apps was resource-intensive and required a lot of processing power.
3. Tracking accuracy: ARKit uses the device's camera and sensors to track the real-world environment. The accuracy of the tracking can be affected by factors such as lighting conditions, camera calibration, and the environment. We had to ensure that the app was tested adequate lighting conditions.
4. User interface design: The user interface of an AR app can be challenging to design as it needs to provide an intuitive and natural way for users to interact with the AR environment.
5. 3D asset creation: AR apps often require 3D assets for objects and animations. Creating 3D assets that are optimized for AR can be time-consuming and require specialized skills.
6. Testing: Testing an AR app was a little challenging as it requires physical interaction with the real-world environment.
   Overall, building an this AR app was a little challenging task, but it was also a rewarding experience to create an immersive and interactive experience for users.