As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
MAIN TANKS FUEL QUANTIY IMBALANCE LIMIT EXCEEDED @ FL 380 DURING FUEL BALANCE. GROUNDED - YES. PER ACARS REPORT, FUEL IMBALANCE EXCEEDED 1000LBS. NO TURBULENCE, SIGNIFICANT LOAD OR RAPID/LARGE CONTROL INPUT WAS REPORTED. CONDITIONAL INSP NOT REQUIRED PER B737-900 AMM 05-51-48-211-801 TABLE 801.