Hi @suguna and @Davidlin_ch12,
Sorry for the long delay, I was doing some checking on this, and this behavior may be due to a phenomena called FOUT (a flash of unstyled text).
Read more about this here: Quick Tip: Avoid FOUT by Adding a Web Font Preloader
One solution for this is to use a custom style in the Header of the site, to set the html to 0% opacity while the automatic wf-loading class is added by google fonts while loading the fonts.
<style>
html.wf-loading * {
opacity: 0;
}
</style>
After adding the CSS above, then republish the site, and the momentary font fallback should be solved.
I hope this helps!