UART B/C are not communicating with external controller

I’m trying to do serial interface between ESP8266-DevKitC and VF61 using viola plus.
ESP has TTL 3.3V interface.

I have done successful communication from UART A. But i want to do it from UART B. But it is not happening.
I have also tried using UART C, but still no success.
For diagnosis, I have connected UART A and UART B Rx/Tx together to check if UART B is sending and receiving data. It was working fine.

I have tried multiple VFxx boards and multiple carrier boards. But same issue.
I have tested same code with IMX 6 and ESP, it is working perfectly with with UART B/C.

Kindly guide us what we are missing.

Hi @kshah,

This seems to be strange that UART B is able to transmit/receive but not with ESP8266.
Can you check the signals with a logic analyzer/oscilloscope and see the difference between the two while the ESP8266 is connected?