Sometimes the FBI name checks come back and link fragments of a name with FBI files. Then USCIS will conduct additional review on your case. According to the federal codes, service center can withhold a case for up to two years. After that, USCIS can extend the withholding, 6 month each time. So, they can withhold a case indefinitely without violating any law. The federal district courts is barred to review their action under 8 USC 1252