Other service centers also showed a difference, in the https://egov.uscis.gov/processing-times/ there is a note talking about "USCIS service centers are now prioritizing the processing of Form I-130 preference petitions for which an the Department of State Visa Bulletin shows that an immigrant visa is available" so that could be why it changed but who knows. A friend today got approved after it changed last week, her pd is July also potomac