Your theory is correct in that the front camera is not typically the root cause if it functions properly in all modes except for the 360 degree view.
The system actually uses the same circuits for all modes of operation. Each camera has a twisted and shielded pair of video circuits along with power and ground circuits. The system is controlled by the Image Processing Module B (IPM-B), which communicates with the front and rear camera over a LIN bus. The IPM-B generates the image displayed on the screen, including the 360 view. The LIN bus allows the IPM-B and cameras to communicate the following:
- Camera view request
- Camera configuration data
- Display manual zoom request (rear camera only)
- Trailer connection status (if equipped with trailer tow)
- Standby enable/disable request
Since the front camera was already replaced, I'd suspect an issue with the IPM-B. However, the other possibility is a camera quality issue from the supplier that is causing the image issue when the IPM-B requests the 360 view over the LIN.