Angular Jest async test seems to overflow results from one test to another

In Angular, using Jest we have 2 tests that test a method on a component class:

  describe('checkEmailStatus', () => {
    it('set VERIFIED page design when email verification succeeds', async () => {
      jest.spyOn(authService, 'checkEmailVerification');
      await expect(component.checkEmailStatus()).resolves.toEqual(undefined);
      expect(authService.checkEmailVerification).toBeCalledTimes(1);
      expect(component.pageDesign.key).toBe('verified');
    });

    it('set ERROR page design when email verification fails', async () => {
      const checkEmail = jest.spyOn(authService, 'checkEmailVerification');
      checkEmail.mockImplementation(() => {
        return Promise.reject(false);
      });
      await expect(component.checkEmailStatus()).resolves.toEqual(undefined);
      expect(authService.checkEmailVerification).toBeCalledTimes(1);
      expect(component.pageDesign.key).toBe('error');
    });
  });

These tests have been running fine for a month. Nothing about this component has changed and neither have we changed Jest version (25.2.7) yet now the 2nd test complains that the method was called 3 times.

If I comment out the first test, the 2nd tests passes.

It seems that the first test is not tearing down correctly - is there something I need to do to force that? (I tried using the done() callback, but it made no difference)

UPDATE

This is the method under test:

  async checkEmailStatus(): Promise<void> {
    this.isLoading = true;
    try {
      await this.authService.checkEmailVerification('');
      this.setPageDesign('verified');
      this.isLoading = false;
    } catch (error) {
      this.setPageDesign('error');
      this.isLoading = false;
    }
  }

This is the stubbed authService:

import {Observable, BehaviorSubject, of} from 'rxjs';
import {switchMap} from 'rxjs/operators';
import {mockUsers} from '../../../../mocks/user.mock';

// tslint:disable-next-line: completed-docs
function initStub() {
  const userId$ = new BehaviorSubject<string>(null);

  return {
    userId$,
    checkEmailVerification(): Promise<boolean> {
      return Promise.resolve(true);
    }
  };
}

export const authServiceStub = initStub();