I have seen this crop up on several sites we host (all running 6.2.1.1). So far, the CSS text above the header seems to be visible only when logged out – which of course, would be most site users.
I went into the Weaver Xtreme Admin (not the Customizer) > Main Options > Menus, and found a few places where CSS had the – sign instead of the + sign (but no custom CSS code entered). I clicked to change it back to the +, and that fixed the display problem! Then on one site, I saw only /* CSS */ above the header, but found no instances of the ‘CSS – ‘ in the menu or any other settings. I clicked the + twice for each of those options on the menu settings page, saved it, and the text went away.
I have so far been unable to recreate the problem – I have tried clicking CSS + to expand it to CSS – and saving without adding any code, but nothing happens. So I’m nut sure where this comes from, but for me at least, it has been an easy fix when I run across it!