In short, there is nothing wrong. You will only see these messages when you have Chrome’s dev tools open.

Many Mendix widgets are built using tools that minify the JavaScript in them to reduce the size of the file that has to be loaded in your browser. Debugging a minified file as a human is really hard, so there’s also the concept of a “map” file which your browser can use to transform the file back into its original form for debugging purposes. When you have Chrome dev tools open and Chrome detects a minified file, it will try to automatically load the map file. This map file is only included while building and debugging the widget, but is not included in release/production builds of the widget (by design). So, you get a 404 when Chrome fails to find the map file.

For more info, read here: https://blog.praveen.science/avoiding-http-404-for-map-files-when-using-minified-css/