Thesrc/components/avatar/_avatar.scss file contains

a,.btn {&.b-avatar:hover:not(.disabled):not(disabled) {z-index:1;    }  }

anddisabled is not a valid selector in:not(disabled).

I believe it should be:not([disabled]) which means "element does not have thedisabled attribute".

a,.btn {&.b-avatar:hover:not(.disabled):not([disabled]) {z-index:1;    }  }