Home Assistant Cast - Custom Icons

While casting views to my Google Home Display, my custom icons are not being displayed. I have Font Awesome installed through HACS as well as Font Awesome Pro icons added to the custom_icons directory manually.

They are working properly through HA, companion app, locally and through Nabu Casa, just not when casting to Google Home displays.

Does anyone know why this would happen? Do they need to be exposed outside of HA, or another way to allow the Google Home Display to access them?