DevTools failed to load sourcemap: Could not load content for http://localhost:8000/vendor/bootstrap-4.1/popper.min.js.map: HTTP error: status code 404, net::ERR_HTTP_RESPONSE_CODE_FAILURE code example

Example 1: DevTools failed to load SourceMap: Could not load content for bootstrap.min.css.map

Delete /*# sourceMappingURL=bootstrap.min.css.map */ in css/bootstrap.min.css
and delete /*# sourceMappingURL=bootstrap.css.map */ in css/bootstrap.css

It is working for me.
I hope it will work for you also.
Namaste _/\_

Example 2: DevTools failed to load SourceMap: Could not load content for http://127.0.0.1:8000/bootstrap-select.min.js.map:

You need to go into Dev Tools settings and you need to unckeck 
"Enable JavaScript source maps"
"Enable CSS source maps"