Angular update from 8.2 to 9.1 --> Angular Material error: 'mat-radio-button' is not a known element

Question

I have just performed an Angular update and have been receiving the following error messages regarding angular material since then:

Error occurs in the template of component LanguageChangeComponent. src /app/common/language-change/language-change.component.html: 9: 9 - error NG8001: 'mat-radio-button' is not a known element:

1. If 'mat-radio-button' is an Angular component, then verify that it is part of this module.
2. If 'mat-radio-button' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message.

I think the module has been imported correctly, but the error message does not go away. What am I doing wrong?

The component looks like this (template):

<my-sidebar class="language-selection">
  <div class="header">
    <span>{{ cfg.title }}</span>
  </div>
  <div class="language-selection-radio-buttons">
    <section>
      <mat-radio-group [(ngModel)]="languageSelection">
        <mat-radio-button value="en" [checked]="languageSelection === 'en'">Englisch</mat-radio-button>
        <mat-radio-button value="de" [checked]="languageSelection === 'de'">Deutsch</mat-radio-button>
      </mat-radio-group>
    </section>
  </div>
  <div class="buttons">
    <button class="button-primary" (click)="changeDefaultLanguage()">change</button>
  </div>
</my-sidebar>

The associated module like this:

import { CommonModule } from '@angular/common';
import { LanguageChangeComponent } from './language-change.component';
import { MySideBarModule } from '@my-sidebar/core';
import { FormsModule } from '@angular/forms';
import { TranslateModule } from '@ngx-translate/core';
import { MatRadioModule } from '@angular/material/radio';

@NgModule({
  imports: [
    CommonModule,
    MySideBarModule,
    MatRadioModule,
    FormsModule,
    TranslateModule
  ],
  declarations: [
    LanguageChangeComponent
  ],
  exports: [
    LanguageChangeComponent
  ]
})
export class LanguageChangeModule { }

Here is an excerpt from my package.json:

  "dependencies": {
    "@angular/animations": "^9.1.12",
    "@angular/cdk": "^9.2.4",
    "@angular/common": "~9.1.12",
    "@angular/compiler": "~9.1.12",
    "@angular/core": "~9.1.12",
    "@angular/flex-layout": "^9.0.0-beta.31",
    "@angular/forms": "~9.1.12",
    "@angular/material": "^9.2.4",
    "@angular/platform-browser": "~9.1.12",
    "@angular/platform-browser-dynamic": "~9.1.12",
    "@angular/router": "~9.1.12",
    "@auth0/angular-jwt": "^5.0.1",
    "@azure/msal-angular": "^1.0.0",
    "@juggle/resize-observer": "^3.2.0",
    "@microsoft/signalr": "^3.1.8",
    "@ngx-translate/core": "^12.1.2",
    "@ngx-translate/http-loader": "^4.0.0",
    "angular-gridster2": "^8.3.0",
    "angular-resize-event": "^1.2.1",
    "azure-maps-control": "^2.0.26",
    "classlist.js": "^1.1.20150312",
    "lodash": "^4.17.15",
    "moment": "^2.29.0",
    "msal": "^1.3.2",
    "ng-dynamic-component": "^5.0.6",
    "ngx-json-viewer": "^2.4.0",
    "ngx-simple-modal": "^1.4.11",
    "rxjs": "~6.5.2",
    "tslib": "^1.10.0",
    "zone.js": "~0.10.2"
  },
  "devDependencies": {
    "@angular-devkit/build-angular": "~0.901.12",
    "@angular/cli": "~9.1.12",
    "@angular/compiler-cli": "~9.1.12",
    "@angularclass/hmr": "^2.1.3",
    "@compodoc/compodoc": "^1.1.9",
    "@types/jasmine": "~3.5.0",
    "@types/jasminewd2": "~2.0.3",
    "@types/lodash": "^4.14.155",
    "@types/node": "^12.11.1",
    "@types/webpack-env": "^1.14.0",
    "codelyzer": "^5.1.2",
    "cpx": "^1.5.0",
    "jasmine-core": "~3.5.0",
    "jasmine-reporters": "^2.3.2",
    "jasmine-spec-reporter": "~4.2.1",
    "karma": "~5.0.0",
    "karma-chrome-launcher": "~3.1.0",
    "karma-cli": "~2.0.0",
    "karma-coverage-istanbul-reporter": "~2.1.0",
    "karma-jasmine": "~3.0.1",
    "karma-jasmine-html-reporter": "^1.4.2",
    "karma-junit-reporter": "^1.2.0",
    "protractor": "~7.0.0",
    "protractor-console-plugin": "^0.1.1",
    "puppeteer": "^1.17.0",
    "ts-node": "~8.3.0",
    "tslint": "~6.1.0",
    "typescript": "~3.8.3"
  }

Answer 1

Had the same issue, so I stopped the project, re-ran npm i, and was able to import MatRadioModule into app-modules.ts.