Hello,
I am not able to reproduce the warning “Failed to parse SourceMap” in Chrome or Chromium, but I wouldn’t worry about it. You only need map files if you are interested in debugging the JavaScript libraries. You could try and delete these two map files to hide the warning.
You also have some JavaScript errors in your console. They do not look like they come from one of the dashed-slug plugins but the errors may interfere with the UI. If you see any problems with the UI, perhaps you should track this error down.
with regards