Unable to use Serial Commands in SDC2160 properly

I am trying to connect my SDC2160 Controller using RS232, When connecting through Roborun+ utility it works fine.

I want to give input through my custom software, which I wrote in python, Issue I am facing is that sometimes the commands I send works properly, other times they don't at all.

Moreover, the !G command to set Motor Command doesn't work at all, even !M command is working in a funny manner whenever it is, like sometimes only one motor moves, sometimes both.

Is there something I am missing? Kindly help me in regards to serial documentation.