I use a Robotdyn, uno+wifi r3 atmega328p+esp8266.It was functioning fine. I had got the esp and the uno to communicate, and anything I wanted logs for, I got them over the web server, both for uno and esp. Strangely, the serial communication with esp has stopped. So, I changed the setting to check esp's serial communication separately. What ever I tried to put to esp using serial monitor does not seem to reach it and vice versa. I tired the same exercise with uno, and it seems to work perfect.
I've verified the switch connectivity in the board, it does not seem to have a problem. Most of the posts online seems to explain the basics of serial connectivity based on the table provided for serial communication by robotdyn.
I do not have an idea, how to debug this further. Any leads would be very helpful.