Problem using two cameras

Hello!
I’m trying to use two different cameras on a python project, using CV2. One is an ‘onboard’ camera, with IMX219 chip. The other is a USB thermal camera. When I use each of them separately, they work fine. But when I try to open the CSI Camera with the USB camera plugged, It doesn’t work. When I try this:

DISPLAY=:0.0 gst-launch-1.0 nvarguscamerasrc  ! 'video/x-raw(memory:NVMM), width=320, height=240, format=(string)NV12, framerate=(fraction)20/1' ! nvoverlaysink -e

It says something like:

(Argus) Error EndOfFile: Unexpected error in reading socket (in src/rpc/socket/client/ClientSocketManager.cpp, function recvThreadCore(), line 266)
(Argus) Error EndOfFile: Receive worker failure, notifying 1 waiting threads (in src/rpc/socket/client/ClientSocketManager.cpp, function recvThreadCore(), line 340)
(Argus) Error InvalidState: Argus client is exiting with 1 outstanding client threads (in src/rpc/socket/client/ClientSocketManager.cpp, function recvThreadCore(), line 357)

The curious thing is that sometimes it works, and I can run the two cameras together… but only sometimes. I’ve tried to find information about the parameters of this command. How can I specify a particular camera if there is more than one?

Thanks in advance for any light you can offer to me.

How do you open the CSI Camera with the USB camera plugged?