Which version of the ESP8266 board manager are you using?  I am using 2.4.2 which is said to be stable, and seems what others have used with the MKS.

Could you post a picture of your wiring of the WeMos to the MKS?

And you are sure you have Serial C enabled with baud rate of 9600?  You could copy you Config.h file for others here to review.