This is the same as:
https://www.vaultwiki.org/issues/6099/
Your style customizations have changed from the default XenForo icon font "Font Awesome" to a different font "Material Icon Designs", and have removed Font Awesome from the list of fonts that should be loaded.
Apart from potential licensing issues, the code points in Material Icon Designs do not match the code points in Font Awesome, so you cannot simply replace the font names with each other.
You will need to update your style changes so that the Font Awesome file continues to be loaded.