I get an error when compiling Fontawesome from scss, why?

Question

Fonts

I have a problem and I don’t understand where it comes from, before that it always worked.

In the scss file, I include the font fontawesome like this:

$fa-font-path: "../../webfonts";
@import "../Libraries/fontawesome-free-5.13.0-web/scss/fontawesome.scss";
@import "../Libraries/fontawesome-free-5.13.0-web/scss/solid.scss";

The style file is compiled in /asssets/css/styles.css
And the fonts are in /assets/webfonts
When compiling, all class names are present, but the Value looks like this

.fa-plus:before {
  content: ""; }

What is the problem?