I just got the same thing here. I asked them for the reason, and they said this:"We understand your concern regarding this investigation. However, your account is still under investigation and no action has been taken against it at this time. We are investigating your apps, account, and any related accounts to ensure compliance with the App Store Review Guidelines, Developer Code of Conduct, and Apple Developer Program License Agreement.Once we have completed our investigation, we will notify you via Resolution Center of any next steps. Due to the nature of the investigation you will be ineligible to receive an expedited review until the investigation is completed.If we require any additional information about your app or account, we will contact you. We appreciate your continued patience during our investigation."I don't know if my app actually got rejected or its just their process of vetting out new developers. I purchased the annual developer license not too long ago, and then like a day later, I submitted my app. Maybe this caused a red flag in their system to check my account?