USCIS sometimes transfers cases between the five service centers in order to balance workload and promote timely processing.
USCIS on April 16, 2018 transferred some of the Form I-601A, Application for Provisional Unlawful Presence Waiver from the Nebraska Service Center to the Potomac Service Center.
For more details on Workload Transfer Updates please visit this link: https://www.uscis.gov/workload-transfers