npm run prod fails with Bootstrap

Can anyone explain to me what is going wrong here and how to fix it? The problem only occurs when I compile for production npm run prod never when I compile for development npm run dev, so it must be something to do with the minifications.

As code:

ERROR in ./resources/sass/app.scss (./node_modules/css-loader??ref--5-2!./node_modules/postcss-loader/src??postcss0!./node_modules/resolve-url-loader??ref--5-4!./node_modules/sass-loader/dist/cjs.js??ref--5-5!./resources/sass/app.scss)
Module build failed (from ./node_modules/postcss-loader/src/index.js):
SyntaxError

(259:4) Unclosed block

  257 | 
  258 |   .navbar-toggler-icon {
> 259 |     background-image: escape-svg($navbar-light-toggler-icon-bg);
      |    ^
  260 |   }
  261 | 

 @ ./resources/sass/app.scss 2:14-253
npm ERR! code ELIFECYCLE
npm ERR! errno 2
npm ERR! @ production: `cross-env NODE_ENV=production node_modules/webpack/bin/webpack.js --no-progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js`
npm ERR! Exit status 2
npm ERR! 
npm ERR! Failed at the @ production script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /Users/emil/.npm/_logs/2020-01-06T22_26_52_993Z-debug.log
npm ERR! code ELIFECYCLE
npm ERR! errno 2
npm ERR! @ prod: `npm run production`
npm ERR! Exit status 2
npm ERR!