Reporting Efficiently to Proper Officials in Response to Terrorism Act of 2017 or the REPORT Act (Sec. 2) This bill requires the Department of Homeland Security (DHS), the Department of Justice (DOJ), the Federal Bureau of Investigation (FBI), and, as appropriate, the National Counterterrorism Center (NCC), to submit to Congress an unclassified report on an act of terrorism in the United States within one year after the primary government agency completes an investigation of such act. Such requirement shall not apply in instances in which DHS, DOJ, the FBI, or the NCC determines that the information required to be reported could jeopardize an ongoing investigation or prosecution, in which case DHS shall notify Congress prior to the first anniversary of the completion of the investigation. Such a report shall: (1) identify any gaps in national security that could be addressed to prevent future acts of terrorism, and (2) include any recommendations for additional measures that could be taken to improve homeland security.