OK, thank you.

We see that icons are missed time to time when your refresh the window. In the Firefox browser it shows an error saying that fonts are not loaded because of timeout on the server https://gyazo.com/bd03a7a1a673e13c56948f5945a18113
We suggest you to use CDN service like KeyCDN to optimize resources loading.

Also, try to disable font-display option in our Theme Settings -> Performance and don’t use “swap” value. Then regenerate all cache and check how it works again.