I use a 3D camera rig in After Effects. It works just great.
The only problem is it uses a null as the master controller, and if you want to export camera data to Cinema4D you need to use a camera so you need to copy all the keyframe data from the camera rig null to the new AE camera and use that camera in Cinema 4D.
So far so good. I did a test where I animated my camera rig and then copied all its data to a new AE camera, exported that to Cinema 4D and it worked beautifully.
Now I am working on the project for real. I copied my keyframe data from the camera rig null to the camera and guess what, it's very slightly different. Different position and different rotation. Enough to be noticeable.
If I check frame by frame, the camera rig null keyframe values and the camera keyframe values are exactly the same. So I cannot see where the error is creeping in!