ERROR TypeError: Cannot add property 0, object is not extensible (NgRx / FireBase / AngularFire)

Question

I am aware that this issue has been reported several times on StackOverflow, but none of the questions has been answered. I have read all of the comments, but I can still not understand how it relates to my code.

I am trying to add a user document to Firestore using setDoc from AngularFire:

firebase.service.ts

  public addUserDocument(userId: string, data: UserDocument) {
   const usersRef = doc(this._fireStore, 'users', userId);
    return from(setDoc(usersRef, {...data}));
  }

I am calling the addUserDocument in my NgRx effects.

auth.effects.ts

  authSignUp$ = createEffect(
    () =>
      this._actions$.pipe(
        ofType(authSignUp),
        switchMap((formData) =>
          this._firebaseService.signUp(formData.email, formData.password).pipe(
            map(response => ({
              user: response.user,
              displayName: formData.displayName
            }))
          )
        ),
        map(data =>  authSignUpSuccess(data))
      ),
  );

  authSignUpSuccess$ = createEffect(() =>
    this._actions$.pipe(
      ofType(authSignUpSuccess),
      switchMap(data => {
        console.log("adding doc")
        return this._firebaseService.addUserDocument(data.user.uid, {
          metaData: {
            isOnboarded: false
          }
        });
      }),
    ), { dispatch: false });

When trying to sign-up I get the following vendor error:

ERROR TypeError: Cannot add property 0, object is not extensible
    at Array.push (<anonymous>)
    at ObserverProxy.subscribe (vendor.js:62785:20)
    at AuthImpl.registerStateListener (vendor.js:6441:27)
    at AuthImpl.onIdTokenChanged (vendor.js:6294:17)
    at AuthInterop.addAuthTokenListener (vendor.js:15609:35)
    at o (vendor.js:32582:87)
    at vendor.js:32585:24
    at Provider.onInit (vendor.js:127253:7)
    at J.start (vendor.js:32585:12)
    at new $a (vendor.js:51436:295)

However, if I do everything inside of the authSignUp$ effect and pipe the response, it works just fine:

  authSignUp$ = createEffect(
    () => 
    this._actions$.pipe(
      ofType(authSignUp),
      switchMap(
        formData => this._firebaseService.signUp(formData.email, formData.password).pipe(
          tap((response) => this._firebaseService.addUserDocument(response.user.uid, {
            metaData: {
              isOnboarded: false
            }
          }
            ))
        )
      )
    ),
    {dispatch: false}
  );

Is there something wrong with the vendor package, or is there something wrong with my code?

Thank you very much for your help.