While testing a site with the @gantry 5 template via @google PageSpeed Insights, I found the following errors related to the fonts (Google fonts):

Ensure text remains visible during webfont load
Leverage the font-display CSS feature to ensure text is user-visible while webfonts are loading. Learn more about font-display.

How to avoid showing invisible text

The font-display API indicates how a font is displayed when used inside a font-face style. The following font-display values will tell the browser to use a system font if the custom font is not ready:

• swap
• optional
• fallback

CSS Example

@font-face {
  font-family: 'Pacifico';
  font-style: normal;
  font-weight: 400;
  src: local('Pacifico Regular'), local('Pacifico-Regular'),
    url(https://fonts.gstatic.com/s/pacifico/v12/FwZY7-Qmy14u9lezJ-6H6MmBp0u-.woff2)
      format('woff2');
  font-display: swap;
}

Google Fonts Example

Add the &display=swap/&display=optional/&display=fallback parameter to the end of your Google Fonts URL:

<link
  href="https://fonts.googleapis.com/css?family=Roboto:400,700&display=swap"
  rel="stylesheet"
/>

Joomla 5.2, Gantry 5.5.19