Hi,
In some condition, the print is shown when there is no frames from the camera source, so it is very likely the cameras are not stable. You may try the gst-launch-1.0 command and see if the issue is present:
gst-launch-1.0 nvarguscamerasrc sensor-id=0 ! fakesink nvarguscamerasrc sensor-id=1 ! fakesink nvarguscamerasrc sensor-id=2 ! fakesink nvarguscamerasrc sensor-id=3 ! fakesink
If the issue is present in both gst-launch-1.0 command and using CameraPipeline, would suggest check the sensor driver to improve stability.