Unit test fails every once in a while when run in a group

The following test that verifies a call to another function fails every once in a while when run as a group. I've used the Moq framework to perform the mocking. Could someone help regarding this? I have no global variables or shared variables.

    public void CallOnceNotificationBLForEmailSendTest()
    {
        Mock<INotificationBL> notificationBLmock = new Mock<INotificationBL>();
        Item processItem = CreateItem(DateTime.Now, ItemDates.End, Process, "TestProcess");
        SaveItem(processItem);

        Item mailRecipientItem1 = CreateItem(DateTime.Now, ItemDates.End, MailRecipient, "TestMailRecipient1");
        mailRecipientItem1.SetPropertyValue("EMAIL", DateTime.Now, ItemDates.End, "xyz@slb.com");
        SaveItem(mailRecipientItem1);

        ItemLink proc_mailrec = new ItemLink("PRC_RECIPIENT", processItem, mailRecipientItem1, DateTime.Now,
            ItemDates.End);
        SaveLink(proc_mailrec);

        ProcessEmailBL processEmailBL = new ProcessEmailBL();
        processEmailBL.NotificationBL = notificationBLmock.Object;
        ProcessParameter processParameter = new ProcessParameter
        {
            StartDate = ItemDates.Start,
            EndDate = ItemDates.End,
            ProcessItem = processItem
        };
        processEmailBL.SendEmail(processParameter, processItem, It.IsAny<DateTime>(), It.IsAny<string>(),
            It.IsAny<string>());

        notificationBLmock.Verify(
            x => x.SendAndQueueMail(It.IsAny<List<string>>(), It.IsAny<string>(), It.IsAny<string>(),
                It.IsAny<string>(), It.IsAny<Attachment>(), It.IsAny<string>()), Times.Exactly(1));
    }