Hi Neil,
Nothing to worry, it's crazy Bootstrap default code. Not needed files.
Edit this file: templates\nuron\js\bootstrap.bundle.min.js
and remove/delete comment line at the very bottom
//# sourceMappingURL=bootstrap.bundle.min.js.map
This same step inside CSS file:
templates/nuron/css/bootstrap.min.css file, remove comment line at the very bottom.
SAVE changes, clear Joomla cache and that's all in 90sec.
In general files from comments shouldn't be loaded even requested, but somehow ... you know ://