@Yoshimaru-Tanaka ,
Can you please stop voxl-camera-server service and run the camera server in foreground to make sure that all cameras are started:
systemctl stop voxl-camera server
voxl-camera-server
If there is a problem, you should see it in the terminal output. I am surprised that voxl-inspect-cam -a does not produce any output, which means none of the cameras are alive, so you should see something in the output from voxl-camera-server process.
Perhaps your board is not correctly configured for the cameras, so you may want to run voxl-configure-cameras and select the correct option for your camera setup. Then re-start voxl-camera-server.
Alex