Angular 9: Value at position X in the NgModule.imports is not a reference

In my case the issue was related to an imported library, that was not Angular v9 compatible (among other things it was not using deep links to Angular Material and moment.js).

I was lucky as the library is an intern one and I could fix these points and republish it. After that it built without any problems or changes on my project side.

you might have used npm i and the editor might fail to generate the build correctly. Try restarting your editor. Restarting worked for me. I was using VSCode

you need to change your custom build of modules, so you need to make analog changes to the ones below, in my case i needed to change:

export class ThemeModule {
  static forRoot(): ModuleWithProviders {
    return <ModuleWithProviders>{
      ngModule: ThemeModule,
      providers: [
        ...NbThemeModule.forRoot(
          {
            name: 'default',
          },
          [DEFAULT_THEME, COSMIC_THEME, CORPORATE_THEME, DARK_THEME],
        ).providers,
      ],
    };
  }
}

to:

export class ThemeModule {
  static forRoot(): ModuleWithProviders<ThemeModule> {
    return {
      ngModule: ThemeModule,
      providers: [
        ...NbThemeModule.forRoot(
          {
            name: 'default',
          },
          [DEFAULT_THEME, COSMIC_THEME, CORPORATE_THEME, DARK_THEME],
        ).providers,
      ],
    };
  }
}