Logged out of servers during a competitive match

Why is it so that I lose a rank and have to serve a suspension when I get kicked of the severs when my wifi is working?

Wifi is never foolproof. It could be that it cut off for a second or two, which could be enough to break your connection. And with how things are all leavers get the same treatment despite the reason.

You could look for trouble shooting options on the technical support.