I was facing same issue. My dev instance working but not the sandbox instance

I called the url of static resource from community to identify the URL which allows to download the font file finally below was my url which downloads the font

https://XXX-XXX-community.csXX.force.com/communityName/s/sfsites/c/resource/resourcename

finally css font definition is

@font-face { font-family: 'fontname'; src: url('/communityName/s/sfsites/c/resource/resourcename') format('woff'); }

Whereas in my dev instance

@font-face { font-family: 'fontname'; src: url('/sfsites/c/resource/resourcename') format('woff');

}

I was facing same issue. My dev instance working but not the sandbox instance

I called the url of static resource from community to identify the URL which allows to download the font file finally below was my url which downloads the font

https://XXX-XXX-community.csXX.force.com/communityName/s/sfsites/c/resource/resourcename

finally css font definition is

@font-face {
    font-family: 'fontname';
    src: url('/communityName/s/sfsites/c/resource/resourcename') format('woff');
}

Whereas in my dev instance

@font-face {
    font-family: 'fontname';
    src: url('/sfsites/c/resource/resourcename') format('woff');
}