My  Razer keyboard worked perfectly until  a month ago when it  started behaving weirdly. 
Some keys  (mostly D, Space and 0), when pressed once  output double or even triple  the  characters.
It  is  happening  right now with my spacebar.

I didn’t have this problem before and I never changed my  PC. 
I have already tried updating the firmware, switching Synapse  versions and even using the Synapse Beta  version.
Nothing worked so I  sent it to a specialist to clean the switches. However that was not the problem. 
It is still double typing and it  is so annoying. 

I read something about  polling rate  online but there is no such option in Synapse for the keyboard,  only for the mouse.