Strange circular USB icon in Finder
I have those now, too. I assumed the sidebar icon had just been changed to those circles in a recent update. 



As far as I know, the default sidebar icons are still located here:

/System/Library/CoreServices/CoreTypes.bundle/Contents/Resources/


You should be able to swap any or all of them out for any icons you want. Just give your new icon the same name as the one you are replacing and make sure it is a .icns file. You will probably need to disable SIP in order to do this. 

EDIT: On closer look, I don't see any dots amongst the default sidebar icons in CoreTypes. I wonder if it may have something to do with disk permissions....