angular.json に "preserveSymlinks": true を追加する。

angular.json

{
  "projects": {
    ...
    "my-app": {
      "architect": {
        ...
        "build": {
            "builder": "@angular-devkit/build-angular:browser",
            "options": {
              "index": "src/index.html",
              "main": "src/main.ts",
              "polyfills": "src/polyfills.ts",
              "tsConfig": "src/tsconfig.app.json",
              ...
              "preserveSymlinks": true
            }
        },
        ...
      }
      ...
    }
    ...
  }
}

以上。

参考

Problem with ng serve --preserve-symlinks Angular/CLI 6.0.0 #10735