DevTools failed to load SourceMap: Could not load content for webpack:///node_modules/react-router/esm/react-router.js.map: HTTP error: status code 404, net::ERR_UNKNOWN_URL_SCHEME 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