TurboTax does not get any information from the IRS after your return is accepted, so no one at TT knows that your return is under review or why. If the IRS wants more information from you they will request it in a letter. For now you know the IRS has your return and is working on it---and that your refund might take longer while they complete their review. You can continue to watch the IRS refund site for information.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**