That's right, sometimes works and sometimes not, if i start a new project the graphic audio meters in the whole project doesn't work.... i hear sound but not visual feedback of any meter
 
 

Problems that can't be reproduced or are intermittent are difficult to troubleshoot.
 
I suggest checking for a graphics/video driver update. You can typically find these on your computer manufacturer's website under support.
 
Another idea is to try a clean boot -- in case something else running on your system is conflicting with Sonar.
 
https://support.microsoft.com/en-us/help/929135/how-to-perform-a-clean-boot-in-windows