Loading issues can cause a FOUC (flash of unstyled content). It really comes down to the way that Elementor embeds its templates. When a page is loading, Elementor cannot recognize which templates have been embedded in the page, and this is why Elementor loads the template stylesheets in the footer.
In some cases, this can cause a small flash (flicker or FOUC) when the page loads.
How To Solve FOUC?
Define the CSS Print Method to be inline instead of using external files. This can be done by going to your WordPress Admin > Elementor > Settings > Advanced > CSS Print Method > Internal Embedding
More on this can be found in “Dealing with flickers/FOUC” via Elementors Documentation.