Hi, my mother's case was approved on July 13, 2023, and was sent to the NVC on July 16, 2023; since then, I haven't received the NVC case creation email (NVC Welcome Letter). I have contacted NVC twice, and they said they hadn't received the approved petition from USCIS yet, although I shared the I-797 approved petition letter with them; when I contacted USCIS, they told me to wait 90 days, if I do not hear back within 90 days then they will resent the petition again, however when father case was approved on June 26, 2023. His case was sent to the NVC on June 30, 2023, I received the NVC welcome letter email within five days after they sent it to NVC, and both cases were approved 17 days apart from each other. National Benefits Center approved my Father's case, and the California service center approved the mother's case; I'm not getting it; what is the cause of this delay? Does anybody in the same situation now or in the past? Please share your experience. Thanks.