By default NitroPack is configured for fast page rendering. By default, browsers will not render text if the font is not loaded yet, which slows down the rendering of pages.
NitroPack instructs the browsers to render text as soon as they can, and then swap the font of the rendered text as soon as the font becomes available. This makes for a very fast page rendering, however the font swap is often visible to the clients. If you want to disable this feature and keep the default browser behavior where text is rendered only after the fonts are loaded you can do the following setting changes in NitroPack in order to achieve this:
Log into your account at https://nitropack.io/
Navigate to the Settings section
Move the optimization mode slider to Manual
Switch to the Advanced Settings tab
Click Additional options under the Optimize CSS Delivery option
Set Remove @font-face rules from the critical CSS to Disabled
Disable the Override font rendering behavior option by using its slider toggle on the right
Save the changes and purge your cache.