I had posted an issue about a month back relating to 3D models disappearing for a few frames and then reappearing. I was working on a new composite shot and ran into the same problem. I think I may have solved the issue but I don't really understand it.
In the new composite shot at the point where the model disappeared, I found that the 'clip window' in the second model's settings was the culprit. The model that disappeared was in 3D Unrolled mode but the second model is set to 3D Plane. When I adjusted the size of the Clip Window in the 2nd 3D plane model, I found the 1st model appeared and stayed visible.
So what is the purpose of the Clip Window and how does it work exactly?