How to check the driver state, I found that only the first time to use udhcpc will appear this problem, and the automatically obtained ip address will not take effect, after the use of udhcpc will not have this problem, I wonder if you have found this problem before
Can you share BSP version? Let me check it on my side.
This is udhcpc command issue, the udhcpc will down the another interface on userspace layer.
When we run the udhcpc command it will disable all the interface,but only enable the one we used currently at last. For the detail information you can reference the /etc/udhcpc.d/50default script. You can enable the other interface using ifconfig tool.
ifconfig eth0/eth1 up