These files are crucial to your site's structure and even though Google might flag them, they have no negative effect on your site.
These errors should not cause you concern, rather, you can learn how to improve your site's loading time.
Understanding your Site
Keep in mind that your site's loading time depends on a number of factors, both local (i.e., related to your local Internet connection) and non-local (i.e., related to your site's design). For example, if you are using a newer computer or a high-speed network, your site may load faster than if you were using an older computer on a low-speed network.
If you feel that your site is loading slowly, the first step is to check whether the issue is local or not. To do so, try accessing your site from different computers on different networks and see if the problem persists.
If you confirm that your site is running slowly on all computers and networks, take a look at the content on your site's home page.
Improving Sites Loading Speed
There is a compromise between site loading time and eye-catching or interactive features. This does not mean that you should not add these features, rather, they should be added in moderation.