I have a subscription method like so and it is working fine.

 setOnboardingUser(uid: string): void {
    this.currentUserUid = uid;

    combineLatest([this.getProfile(uid), this.getUserFirstName(uid), this.getUserLastName(uid)]))
      .subscribe(([res1, res2, res3]) => {
        this.OnboardingUser = res1;
        this.userFirstName = res2.firstName;
        this.userLastName = res3.lastName;
      }, err => { console.log(err); }); // it throws error here when signout
  }

…