DevTools failed to load SourceMap: Could not load content for http://bigcheese.localhost/yassets/ye335784a/ckeditor5/ckeditor.js.map: HTTP error: status code 404, net::ERR_HTTP_RESPONSE_CODE_FAILURE code example

Example: DevTools failed to load SourceMap: Could not load content for

Open Developer Tools, 
go to "Settings" for Developer Tools, 
then uncheck Enable JavaScript Sourcemaps under the "Sources" settings.
Restart Browser if needed