Hi,
You may be using USB2 cameras and the total bandwidth is 480Mbps. There is a similar topic:
connected more than two usb cameras problem on deepstream-app (Jetson Nano Dev Kit) - #12 by DaneLLL
Or the power supply is insufficient and launching two cameras needs current > 2A:
Tegra-xusb 3610000.xhci: ERROR unknown event type 37 - #10 by DaneLLL
Power supply - #4 by Trumany